A roller-coaster car has a mass of 1200 kg when fully
loaded with passengers. As the car passes over the top of a circular
hill of radius 18 m, its speed is not changing. At the top of the
hill, what are the (a) magnitude FN and (b) direction (up or
down) of the normal force on the car from the track if the car’s
speed is v 11 m/s? What are (c) FN and (d) the direction if v
14 m/s?
Final answer:
At the top of the hill, the roller-coaster car experiences a normal force (FN) from the track that is equal to the gravitational force (mg). The direction of the normal force at the top of the hill is downwards. When the car's speed increases to 14 m/s, the magnitude of the normal force remains the same, but its direction stays downwards.
Explanation:
To determine the magnitude of the normal force (FN) and its direction at the top of the hill, we need to consider the forces acting on the roller-coaster car. At the top of the hill, the car's speed is not changing, meaning its acceleration is zero. This means that the net force acting on the car is zero. The only forces acting on the car at the top of the hill are the gravitational force (mg) and the normal force (FN) from the track.
(a) When the car's speed is 11 m/s, we can equate the gravitational force and the normal force:
mg = FN
Using the given mass of 1200 kg, we can calculate the magnitude of the normal force:
FN = mg = 1200 kg * 9.8 m/s^2 = 11760 N
(b) The direction of the normal force at the top of the hill is downwards (towards the center of the circular path), as it opposes the gravitational force pulling the car downwards.
(c) When the car's speed is 14 m/s, the magnitude of the normal force remains the same:
FN = mg = 1200 kg * 9.8 m/s^2 = 11760 N
(d) The direction of the normal force at the top of the hill is still downwards, as it continues to oppose the gravitational force.
(a) At a speed of [tex]\(v = 11 \ m/s\)[/tex], the magnitude of the normal force [tex](\(F_N\))[/tex] on the roller-coaster car at the top of the hill is [tex]\(9810 \ N\)[/tex] (upward).
(b) At a speed of [tex]\(v = 14 \ m/s\)[/tex], the magnitude of the normal force [tex](\(F_N\))[/tex] on the roller-coaster car at the top of the hill is [tex]\(7560 \ N\)[/tex] (downward).
Explanation:In circular motion, at the top of the hill, the centripetal force required to keep the car moving in a circular path is provided by the normal force [tex](\(F_N\)). At \(v = 11 \ m/s\)[/tex], the net force is zero as the car's speed is constant, so [tex]\(F_N\)[/tex] equals the gravitational force [tex](\(mg\))[/tex], resulting in [tex]\(F_N = 9810 \ N\)[/tex] (upward). This is because the normal force opposes the gravitational force and provides the centripetal force needed.
At [tex]\(v = 14 \ m/s\)[/tex], the normal force is directed downward. In this case, the centripetal force is greater than the gravitational force, leading to a net force directed toward the center of the circular path. The normal force now includes both the gravitational force [tex](\(mg\))[/tex] and the additional force required for centripetal acceleration. The magnitude of [tex]\(F_N\) is \(7560 \ N\)[/tex], and it is directed downward as the net force acts in the opposite direction to the gravitational force.
Understanding the dynamics involves recognizing that at different speeds, the balance between gravitational force and the force required for circular motion changes. At lower speeds, the normal force opposes gravity, while at higher speeds, it supplements gravity to provide the necessary centripetal force.
What method of heat transfer does heat energy use to reach earth from the sun?
Answer: Radiation
Explanation:
Heat transfer through radiation. Radiation is one of the mode of heat transfer and is the transfer of heat from one body to another without passing through any intervening medium. It is the heat energy directly from the sun. This energy reaches the earth directly without obstruction.
A basketball player, who weighs 600 newtons, jump 0.5 meters vertically off the floor. Calculate her kinetic energy just before hitting the floor.
a)300J
b)3000J
c)9.81m/s^2
d)0
Answer:
300 J
Explanation:
[tex]v = \sqrt{2gh}[/tex]
[tex]KE = \frac{1}{2}mv^{2}[/tex]
——
[tex]v = \sqrt{2(9.81 m/s^{2})(0.5 m)}\\ v = 3.13[/tex]
[tex]KE = \frac{1}{2}(61.2 kg)(3.13 m/s)^{2}\\ KE = 300 J[/tex]
Kinetic energy of an object is calculated from its mass and velocity. The mass of the player is 61.2 g and the velocity is 3.13 m/s. Then the kinetic energy of the basketball player is 300 J.
What is kinetic energy?Kinetic energy of an object is generated by virtue of its motion. Kinetic energy depends on the mass and velocity of the body by the expression:
K = 1/2 mv².
Given the weight = 600 N
mass = 600 N/9.8 m/s²= 61.2 kg
height = 0.5 m
velocity = √2gh
= √(2×9.8 m/s² × 0.5 m ) = 3.13 m/s
Then, kinetic energy of the player = 1/2 61.2 kg × 3.13 × 3.13
k = 300 J.
Therefore, the kinetic energy of the basketball player is 300 J.
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In A boat race, Dan drove his motorboat over the 1000-meter course from start to finish in 40 seconds. What was Dan's average speed during the race ?
In a boat race, Dan drove his motorboat over the 1000-meter course from start to finish in 40 seconds, and his average speed during the race was 25 meters per second.
What is the calculation of average speed?The average speed indicated that the person maintained a linear speed during a drive because the speed is not always maintained properly due to various factors on the person's path.
Dan's average speed during the race is the distance he covered divided by the time taken to cover the distance.
Dan's average speed during the race was,
Average speed = distance covered / time taken
Average speed = 1000 meters / 40 seconds
Average speed = 25 meters per second
Hence, the average speed during the race was 25 meters per second for Dan while driving the motor boat.
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A train travels at a velocity of +50 m/s. It takes 80 s to slow down to 5 m/s with constant acceleration. What was its acceleration?
two crates, of mass 75kg and 110 kg are in contact and at rest on a horizontal surface. a 730 N force is exerted on a 75kg crate. if the coefficient of kinetic friction is 0.15, calculate (a) the acceleration of the system and (b) the force that each crate exerts on the other.
...?
To calculate the acceleration of the system, use Newton's second law of motion. The force exerted by each crate on the other is equal and opposite.
Explanation:To calculate the acceleration of the system, we need to use Newton's second law of motion, which states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration. The net force acting on the system is the applied force minus the force of friction. So, the acceleration of the system can be calculated as:
Net force = Applied force - Force of friction
F_net = F_applied - F_friction
The force of friction can be calculated using the formula:
Force of friction = coefficient of friction * Normal force
Now, to calculate the force that each crate exerts on the other, we need to consider that the force exerted by one crate on another is equal in magnitude but opposite in direction. So, if we know the force exerted by one crate on the other, we can simply use Newton's third law of motion to find the force exerted by the other crate on the first crate.
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The earth's differentiation and size were significant factors for life on Earth because Earth's composition and gravitational attraction _____.
-keep the moon and sun in orbit
-keep people grounded
-helped to create and retain Earth's atmosphere
-create and retain internal heat
Final answer:
The Earth's differentiation and size have been crucial in maintaining a life-sustaining atmosphere due to its gravitational pull, which helps generate and preserve internal heat, and creates the greenhouse effect for temperature regulation.
Explanation:
The Earth's differentiation and size were critical in forming an environment suitable for life due to a combination of factors, primarily influenced by Earth's mass and gravitational forces. The composition and gravitational attraction of Earth have been instrumental in creating and retaining a protective atmosphere, which in turn has allowed for the development and sustenance of life. Differentiation is a process where gravity separates a planet's interior into layers, with heavier elements forming the core and lighter minerals forming the crust. Consequently, Earth's ability to generate and retain internal heat has contributed to the eventual development of not just an atmosphere, but one that is conducive to life, maintaining a balance of gases such as oxygen and carbon dioxide while shielding the planet from harmful radiation. Additionally, Earth's atmosphere acts as insulation, creating what's known as the greenhouse effect, which helps regulate the planet's temperature, preventing the oceans from freezing.
the captain of a ship views the top of a lighthouse at an angle of 60degree with the horizontal at an elevation of of 6 meters above sea level.five minutes later,the same captain of the ship views the top of the same lighthouse at an angle of 30degree with the horizontal.determine the speed of the ship if the lighthouse is known to be 50 meters above sea level. ...?
The speed of the ship is determined to be approximately 0.17 meters per second.
To determine the speed of the ship, we will need to use trigonometry to find the distances the ship travels over the 5-minute interval.
Given:
The height of the lighthouse (h) is 50 meters.The initial angle of elevation (θ₁) is 60 degrees.The final angle of elevation (θ₂) is 30 degrees.The height of the observer above sea level is 6 meters.First, find the initial horizontal distance (d₁) from the ship to the lighthouse using tan(θ₁):
tan(60°) = height difference / d₁
tan(60°) = (50 m - 6 m) / d₁
d₁ = (44 m) / tan(60°)
d₁ = 44 / √3 ≈ 25.4 meters
Next, find the final horizontal distance (d₂) from the ship to the lighthouse using tan(θ₂):
tan(30°) = height difference / d₂
tan(30°) = (50 m - 6 m) / d₂
d₂ = (44 m) / tan(30°)
[tex]d_2 = \frac{44}{\left( \frac{\sqrt{3}}{3} \right)} = 44 \cdot \sqrt{3} \approx 76.2 \, \text{meters}[/tex]
The distance traveled by the ship (Δd) is:
Δd = d₂ - d₁ ≈ 76.2 m - 25.4 m ≈ 50.8 meters
The time interval Δt is 5 minutes, which is 300 seconds.
Therefore, the speed (v) of the ship is:
v = Δd / Δt ≈ 50.8 m / 300 s ≈ 0.17 meters per second.
A youngster throws a rock from a bridge into the river 50 m below. The rock has a speed of 15 m/s when it leaves the youngster’s hand. Calculate the velocity of the rock when it strikes the water if it is thrown upward.
...?
Which of the following is not a carbohydrate?
A. Cellulose
B. Sugars
C. Starches
D. Cholesterol
The option that is not a carbohydrate is cholestrol, which is the option D.
D. Cholesterol
What is carbohydrate?Carbohydrate are organic compounds that are made of carbon, hydrogen and oxygen atoms, forming polar hydroxyl groups, (-OH). Carbohydrate are an important source of energy in an healthy diet. There are three main types of carbohydrates, namely; sugars, starch, and fibers.
Cholesterol is a waxy, faty chemical substance that is solid and white or light yellow. The chemical formula for cholesterol is C₂₇H₄₆O, hence cholesterol is a lipid, as it has few hydroxyl groups, (-OH)
The other compounds, cellulose, sugars, and starches are carbohydrates
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This is a depiction of 2 forces acting on a puck (top view). Which direction would a 3rd force have to be to balance the forces? [picture below]
If element X has 99 protons, how many elctrons does it have?
Marcel is helping his two children, jacques and gilles, to balance on a seesaw so that they will be able to make it tilt back and forth without the heavier child, jacques, simply sinking to the ground. given that jacques, whose weight is w, is sitting at distance l to the left of the pivot, at what distance l1 should marcel place gilles, whose weight is w, to the right of the pivot to balance the seesaw?
Given that Jacques and Gilles have the same weight, Gilles should sit at the same distance as Jacques from the pivot for the seesaw to be in balance, meaning l1 (the distance for Gilles) equals l (the distance for Jacques).
Explanation:To solve this problem, we must remember that the seesaw is in equilibrium, which means all forces and torques balance out. Here, the principle of moments states that the total clockwise moment must equal the total anticlockwise moment. It implies that, for a seesaw to balance, the weight of each person (considered as force) must be multiplied by their distance from the pivot and the two results obtained must be equal.
Since Jacques and Gilles have the same weight (w), Jacques is sitting at a distance l, the distance l1 at which Gilles should sit is found by equating Jacques' product of weight and distance to Gilles'. Therefore, l1 = l. This confirms the intuition that if they both weigh the same, they should both sit at the same distance from the pivot for the seesaw to be in balance.
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What is the upper block's acceleration if the coefficient of kinetic friction between the block and the table is 0.13?
Let us assume that pulley is mass less.
Let the tension produced at both ends of the pulley is T.
We are asked to calculate the acceleration of the block.
Let the masses of two bodies are denoted as [tex]m_{1} \ and\ m_{2}\ respectively[/tex]
[tex]Let\ m_{1} =1 kg\ and\ m_{2} =2 kg[/tex]
As per this diagram, the body having mass 1 kg is moving downward and the body having mass 2 kg is moving on the surface of the table.
Let the acceleration of each block is a .
For body having mass 1 kg:
The net force acting on 1 kg body will be-
[tex]m_{1} g-T=m_{1} a[/tex] [1]
Here tension in the rope will be vertically upward and weight of the body will be in vertical downward direction.
For body having mass 2 kg:
The coefficient of kinetic friction [tex][\mu]=0.13[/tex]
[tex]Hence\ the\ frictional\ force\ F=\mu N[/tex]
[tex]F=\mu m_{2} g[/tex]
Hence the net force acting on the body having mass 2 kg-
[tex]T-\mu m_{2} g=m_{2} a[/tex] [2]
Here the tension of the rope is towards right i.e along the direction of motion of the 2 kg block and frictional force is towards left.
Combining 1 and 2 we get-
[tex]m_{1} g-T=m_{1}a[/tex] [1]
[tex]T-\mu m_{2}g= m_{2} a[/tex] [2]
---------------------------------------------------
[tex][m_{1} -\mu m_{2} ]g=[m_{1} +m_{2} ]a[/tex]
[tex]a=\frac{m_{1}-\mu m_{2}} {m_{1}+ m_{2}}*g[/tex]
[tex]a=\frac{1-[2*0.13]}{1+2} *9.8\ m/s^2[/tex]
[tex]a=\frac{0.74}{3} *9.8\ m/s^2[/tex]
[tex]a=2.417 m/s[/tex] [ans]
The acceleration of a block subject to kinetic friction is determined by subtracting the force of friction from the gravitational force parallel to the surface and then dividing by the mass of the block. The force of friction is calculated by multiplying the normal force by the coefficient of kinetic friction.
Explanation:The acceleration of a block sliding on a surface with kinetic friction can be found by using Newton's second law, F = m*a, where F is the net force acting on the object, m is the mass, and a is the acceleration. Given that the coefficient of kinetic friction between the block and the table is 0.13, we first need to find the force of friction, which is the product of the coefficient of kinetic friction (μk) and the normal force (N). Assuming that the only forces acting on the block are gravity, the normal force, and friction, the force of friction can be subtracted from the component of the gravitational force along the inclined plane to get the net force. The net force is then divided by the mass of the block to obtain the acceleration.
To solve for acceleration, the following equations are generally used: Ffriction = μk * N and a = (Fgravity, parallel - Ffriction) / m. It's important to note that without the mass of the block or further details of the scenario, we cannot calculate a numeric answer.
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If 3000ft/3 of air crossing an evaporator coil and is cooled from 75F to 55F, what would be the volume of air,in ft/3, exiting the evaporator coil?
The volume of air remains the same before and after passing the evaporator coil, which is 3000 ft³, as change in temperature does not affect the volume of air assuming constant pressure and amount of air.
Explanation:Given that the question is related to air volumes in relation to temperature changes, here we won't experience a change in volume of air due to the cooling process. According to the ideal gas law, assuming constant pressure and amount of air, a decrease in temperature does not change the volume of the air. Therefore, the volume of the air exiting the evaporator coil is still the same as the volume that entered it, which is 3000 ft³.
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To find the volume of air exiting the evaporator coil, you can use the ideal gas law. Plugging in the given values, the volume of air exiting the evaporator coil would be 2200 ft³.
Explanation:To find the volume of air exiting the evaporator coil, we can use the principle of conservation of mass. The initial volume of air is given as 3000 ft³ and the final temperature is 55°F. We can assume that the air behaves ideally, so we can use the ideal gas law to solve for the final volume of air.
Using the ideal gas law:
V1/T1 = V2/T2
Where V1 is the initial volume, T1 is the initial temperature, V2 is the final volume, and T2 is the final temperature.
Plugging in the values:
V2 = (V1 * T2) / T1 = (3000 ft³ * 55°F) / 75°F = 2200 ft³
Therefore, the volume of air exiting the evaporator coil would be
2200 ft³
.
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Which country was the first in the world to launch a mass media campaign in response to population growth?
A)India
B)China
C)Kenya
D)Australia
Which of the following energy forms is associated with an object in motion?
potential energy
elastic potential energy
nonmechanical energy
kinetic energy
The planets are pulled towards the sun by?
A 0.40kg object is attached to a spring constant 160N/m so that the object is allowed to move on a horizontal frictionless surface. The object is released from rest when the sprin g is compressed 0.15m find:
a) the force on the object and b) its acceleration at this instant.
The force on a 0.40kg object attached to a compressed spring is 24N, and its acceleration is 60 m/s^2 based on Hooke's Law and Newton's second law.
Explanation:A 0.40kg object is attached to a spring with a spring constant (k) of 160N/m and is set to move on a horizontal frictionless surface. When the spring is compressed 0.15m, we need to find the force on the object and its acceleration.
Force on the Object
The force exerted by the spring can be calculated using Hooke's Law, which states that the force exerted by a spring is equal to the spring constant times the displacement from equilibrium (F = -kx). Since the displacement (x) is given as 0.15m, and k is 160N/m, the force is:
F = 160N/m * 0.15m = 24N.
Acceleration of the Object
Using Newton's second law (F = ma), the acceleration (a) can be found by dividing the force by the mass of the object. Given that the mass (m) is 0.40kg:
a = F/m = 24N / 0.40kg = 60 m/s2.
Therefore, at the moment the spring is released from being compressed by 0.15m, the force on the object is 24N and its acceleration is 60 m/s2.
a particle is constrained to move along a straight line through O.
it starts initially at D, which is a fixed distance from O in the positive direction&moves at a constant velocity of 4ms^-1 for 15 sec. until; it is 100m from O for a furhter 25 sec, after which it travels in the opposite direction for 20 sec.
the total distance is 180m.
How far from O does the particle stop?
how do i draw a velocity–time graph?
and what is the final displacement of the particle from its initial position? ...?
The particle ends up 20 meters away from point O in the direction opposite to its initial movement, with a net displacement of -20 meters from its initial position. A velocity-time graph for the particle's motion would show constant velocities in positive and negative directions, with a stationary phase in between.
Explanation:The situation described involves a particle's motion along a straight line with a series of movements at different speeds and directions. To solve this question, we break down the motion into segments and analyze each part to determine the final position and displacement of the particle.
The particle moves at a constant velocity of 4 m/s for 15 seconds, covering a distance of 60 m (4 m/s * 15 s).Afterwards, it remains 100m away from O for 25 seconds, which doesn't affect its position.Finally, it moves in the opposite direction for 20 seconds. Without the velocity of this movement specified, we assume it continues at the previously stated velocity of 4 m/s, thus moving 80 m backwards (4 m/s * 20 s).The total movement towards O (+ direction) is 60m and then 80m away from O (- direction), resulting in the particle ending up 20m away from O in the direction opposite to its initial movement.
To draw a velocity-time graph, plot velocity on the y-axis and time on the x-axis. The graph will show a constant positive velocity of 4 m/s for the first 15 seconds, then a stationary phase (velocity = 0) for the next 25 seconds, followed by a constant negative velocity of -4 m/s for the last 20 seconds.
The final displacement of the particle from its initial position is a result of its entire journey, factoring in the direction of movement. Initially, it moved away from its starting point by 60m but then moved back towards it by 80m, resulting in a net displacement of -20m (20 meters in the direction opposite to the initial positive direction).
What two forces can act on an object without touching it??
A force
F acts in the x - direction, its magnitude given by F = ax^2, where x is in meters and a =5.0N/m^2
. Find the work done by this force as it acts on a particle moving from x = 0 to x = 6.0 m.
The work done by a force can be calculated using the formula W = ∫F dx. In this case, we need to integrate the force function F = ax^2 and substitute the given values to find the work done.
Explanation:The work done by a force can be calculated using the formula:
W = ∫F dx
In this case, the force acting in the x-direction is given by F = ax^2. To find the work done by this force as the particle moves from x = 0 to x = 6.0 m, we need to integrate the force function with respect to x over the given range.
Using the formula for work, we have:
W = ∫(ax^2) dx
Integrating with respect to x, we get:
W = (a/3)x^3
Substituting the values of a and x, we can calculate the work done.
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Surface waves move only in a back and forth motion.
True
False
What is the purpose of the universal gravitation constant in newtons law of universal gravitation?
Explanation : According to the law, it says that F ∝ Mm ÷ R²
Where :
F = Gravitational forceM = Mass of the first bodym = mass of the second bodyR = Distance between the 2 bodiesFor calculating the gravitational force (F), we must have an equation. According to the law, we are ain't getting any equation. Hence, we must convert it by putting a constant.
A constant is any value that is fixed, and it won't change under any circumstance. And in this case, the value of the gravitational constant (G) is 6.67 x 10⁻¹¹.
Now, here comes the final equation : F = GMm ÷ R²
Where :
F = Gravitational forceG = Gravitational constant (6.67 x 10⁻¹¹)M = Mass of the first bodym = Mass of the second bodyR = Distance between the 2 bodiesHence, the main purpose of the universal gravitational constant (G) is to have an equation, which is F = GMm ÷ R².
What is newton's first law of motion?
Answer:
If a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.
Explanation:
Which of the following statements is true about solar eclipses?
There is a solar eclipse every month.
All solar eclipses are total.
Some solar eclipses are not total.
There can be 12 solar eclipses in a single year.
Which element(s) is/are not balanced in this equation?
MgO+2 LiCI → MgCI2+Li2O
A.All elements are balanced
B.Mg
C.CI
D.Li
If the kinetic and potential energy in a system are equal, then the potential energy increases. What happens as a result?
If potential energy in a system increases while its total mechanical energy remains constant, kinetic energy decreases equivalently. This exchange between kinetic and potential energy is an example of the conservation of mechanical energy. Changes in internal energy may also manifest as a change in temperature or energy within the system's structure.
When the potential energy in a system increases without a change in the mechanical energy (assuming no energy is lost to friction), the kinetic energy would decrease equivalently to conserve the total mechanical energy of the system. This is in accordance with the principle of conservation of energy. If an object, for example, is at a certain height above the ground and it is raised further, its potential energy increases due to its position. Consequently, if the object is in free fall, as the potential energy decreases, the kinetic energy increases until the object reaches ground level, where potential energy is at its minimum while kinetic energy is at its maximum.
When the potential energy in a system increases with kinetic energy being equal, it means the internal energy of the system is rising. This increase can be due to an increase in internal potential energy, internal kinetic energy, or both. The work done on the system equals the increase in internal energy.
Moreover, any increase in a system's internal energy that does not result in elevation or speed gain could translate to an increase in internal potential energy or internal kinetic energy, or both. An increase in the internal kinetic energy would generally be observed as an increase in temperature, while an increase in internal potential energy might be observed as energy stored within the structural or molecular configuration of the system.
If we apply this to the scenario of a child on a swing, as the child swings downward, the potential energy (due to height) decreases while kinetic energy increases. Conversely, as the child swings upward, the kinetic energy decreases and potential energy increases.
Fine grains of beach sand are assumed to be
spheres of radius 38.9 µm. These grains are
made of silicon dioxide which has a density of
2600 kg/m3
.
What is the mass of each grain of sand?
Answer in units of kg.
...?
(Newton's Law of Motion) A person stands on a scale in an elevator. When the elevator is at rest, the scale reads 700 N. When the elevator starts to move, the scale reads 600N. (a) Is the elevator going up or down? Show your solution to support your answer. (b) What is its acceleration? ...?
The elevator is accelerating downward as the scale reads less than the person's weight. The acceleration of the elevator can be calculated using Newton's second law of motion and is approximately 1.4 m/s² downward.
Explanation:When a person stands on a scale in an elevator, the scale reading reflects the normal force, which is the force exerted by the scale on the person. If the scale reads 700 N when at rest and only 600 N when the elevator starts to move, it indicates that the elevator is accelerating downward.
This is because the normal force (and thus the scale reading) is less than the person's weight, which would only happen if the force due to acceleration opposes the force of gravity.
For part (b), to find the acceleration of the elevator, we can use Newton's second law of motion. The net force on the person can be calculated by subtracting the scale reading (the normal force) from the person's weight (gravitational force). Let m be the mass of the person and a be the acceleration. We have:
mg - FN = ma
Since mg is the weight (700 N) and FN is the scale reading (600 N):
700 N - 600 N = ma
100 N = ma
Using the given weight of 700 N and the acceleration due to gravity (9.8 m/s2), we find the mass m = 700 N / 9.8 m/s2 = approximately 71.43 kg.
Therefore, the equation becomes:
100 N = 71.43 kg * a
The acceleration a is about 1.4 m/s2 downward.