Physics - Unit 3-5 Practice

A conveyor belt ramp of length 7m is inclined at 20° with respect to the horizontal and is used to move objects from one location to another location. When an object is placed on the conveyor belt, the object travels up the incline with a constant speed of 1.5 ms . A motor is used to keep the conveyor belt moving. The mass of the objects that are placed on the conveyor belt are varied. Suppose the motor breaks and a person must push an object of mass 30kg from the bottom of the incline to the top of the incline. The person can exert a force of 150N on the object parallel to the incline. What is the approximate amount of work that the person does on the object to move it to the top of the incline? Assume that all frictional forces are negligible. A) 0 J B) 239 J C) 658 J D) 1050 J

239 J

A block of mass 3 kg slides along a horizontal surface that has negligible friction except for one section, as shown above. The block arrives at the rough section with a speed of 5 m/s and leaves it 0.5 s later with a speed of 3 m/s. What is the magnitude of the work done by the frictional force exerted on the block by the rough section of the surface? A) 24 J B) 16 J C) 8 J D) 6 J E) 3 J

24 J

A block on a horizontal surface is placed in contact with a light spring with spring constant k, as shown in Figure 1. When the block is moved to the left so that the spring is compressed a distance d from its equilibrium length, the potential energy stored in the spring-block system is Em . When a second block of mass 2m is placed on the same surface and the spring is compressed a distance 2d, as shown in Figure 2, how much potential energy is stored in the spring compared to the original potential energy Em ? All frictional forces are considered to be negligible. A) 1/2Em B) Em C) 2Em D) 4Em

4Em

Planet X has twice Earth's mass and three times Earth's radius. The magnitude of the gravitational field near Planet X's surface is most nearly A) 2 N/kg B) 7 N/kg C) 10 N/kg D) 20 N/kg

A) 2 N/kg

While traveling in its elliptical orbit around the Sun, Mars gains speed during the part of the orbit where it is getting closer to the Sun. Which of the following can be used to explain this gain in speed? A) As Mars gets closer to the Sun, the Mars-Sun system loses potential energy and Mars gains kinetic energy. B) A component of the gravitational force exerted on Mars is perpendicular to the direction of motion, causing an acceleration and hence a gain in speed along that direction. C) The torque exerted on Mars by the Sun during this segment of the orbit increases the Mars-Sun system's angular momentum. D) The centripetal force exerted on Mars is greater than the gravitational force during this segment of the orbit, causing Mars to gain speed as it gets closer to the Sun.

A) As Mars gets closer to the Sun, the Mars-Sun system loses potential energy and Mars gains kinetic energy.

The figure above shows the net force exerted on an object as a function of the position of the object. The object starts from rest at position x = 0 m and acquires a speed of 3.0 m / s after traveling a distance of 0.090 m. What is the mass of the object? A) .015 kg B) .030 kg C) .045 kg D) .060 kg

B) .030 kg

A student must determine a nonzero change in momentum of an object for a specific interval of time. Which of the following experiments could the student conduct? Select two answers. A) Drop a ball of known mass above a motion detector, and record the final speed of the ball before it reaches the motion sensor. B) Drop a coffee filter of known mass from a known height above a motion sensor, and record the terminal speed of the coffee filter as it falls. C) Pull a block of known mass across a rough surface with a spring such that the block travels at a constant speed for 5s as measured by a stopwatch. Record the force necessary to pull the block at a constant speed. D) Give a block of known mass an initial velocity so that it slides across a rough surface in front of a motion detector, slows down, and eventually stops. Use the motion detector to record the initial velocity of the block.

A) Drop a ball of known mass above a motion detector, and record the final speed of the ball before it reaches the motion sensor. D) Give a block of known mass an initial velocity so that it slides across a rough surface in front of a motion detector, slows down, and eventually stops. Use the motion detector to record the initial velocity of the block.

One end of a string is attached to the ceiling with the other end attached to a toy. The toy can be set into motion such that it travels in a horizontal circular path at a constant tangential speed, as shown above. Which of the following measuring tools, when used together, could be used to determine the time it takes for the toy to complete one revolution around the circle? Select two answers. A) Protractor B) Meterstick C) Force probe D) Motion sensor

A) Protractor B) Meterstick

A student is conducting an experiment to analyze the mechanical energy of a block-spring system. The student places a block of mass 2kg on a horizontal surface and attaches the block to a horizontal spring of negligible mass and spring constant 100N/m, as shown in the figure. There is negligible friction between the block and the horizontal surface. The other end of the spring is attached to a wall. The block-spring system is initially at the spring's equilibrium position. Based on data collected from the experiment, the student creates the graph that shows the force exerted on the spring as a function of the distance the spring is compressed. How can the student use the data to experimentally determine the work done on the spring by the block? A) Determine the slope of the line of best fit through the data from 0.0 m0.0 m to 1.0 m1.0 m. B) Determine the area bound by the line of best fit through the data and the horizontal axis from 0.0 m0.0 m to 1.0 m1.0 m. C) Use the maximum value of the force exerted on the spring and multiply that value by the maximum distance that the spring is compressed. D) This graph cannot be used to determine the work done by the block on the spring because the force exerted on the spring by the block is not constant.

B) Determine the area bound by the line of best fit through the data and the horizontal axis from 0.0 m0.0 m to 1.0 m1.0 m.

The pendulum illustrated above has a length of 2 m and a bob of mass 0.04 kg. It is held at an angle Ѳ, as shown, where cosѲ = 0.9. If the pendulum is released from rest, the maximum speed the bob attains is most nearly A) 1 m/s B) √2 m/s C) 2 m/s D) 4 m/s E) 6 m/s

C) 2 m/s

A student on another planet has two identical spheres, each of mass 0.6 kg, attached to the ends of a rod of negligible mass. The student gives the assembly a rotation in the vertical plane and then releases it so it falls, as shown in the top figure above. Sensors record the vertical velocity of the two spheres, and the data is shown in the graph of velocity v as a function of time t. Another student wants to calculate the assembly's angular speed and the change in the linear momentum of the center of mass of the assembly between 0 s and 0.3 s. Which of these quantities can be determined using the graph? A) Angular speed only B) Change in linear momentum only C) Angular speed and change in linear momentum D) Neither of these quantities can be determined using the graph.

C) Angular speed and change in linear momentum

Which of the following is true of the conservation of momentum and kinetic energy? A) Momentum is conserved only in elastic collisions. B) Momentum is conserved only in inelastic collisions. C) Kinetic energy is conserved only in elastic collisions. D) Kinetic energy is conserved only in inelastic collisions. E) Both require the same conditions in order to be conserved.

C) Kinetic energy is conserved only in elastic collisions.

A spaceship travels from a planet to a moon and passes through the three positions A, B, and C, shown above. Position B is midway between the centers of the planet and the moon. The planet has a larger mass than the moon. At which location could the net gravitational force exerted on the spaceship be approximately zero? A) Position A B) Position B C) Position C D) It cannot be determined without knowing the masses of the planet, the moon, and the spaceship, and the exact distance the spaceship is from the planet and the moon.

C) Position C

An inclined track is secured to a table. The height of the highest point of the track above the tabletop is h1. The height from the tabletop to the floor is h2. A block of mass M is released from rest and slides down the track such that all frictional forces are considered to be negligible. The block leaves the track horizontally and strikes the ground at a distance D from the edge of the track as shown. Which of the following statements is correct about the scenario? Select two answers. A) If the block is released from a height 2h1, the block will land at a distance 2D away from the end of the track. B) If the block's mass is increased to 2M2M, the block will land at a distance 2D2D away from the edge of the track. C) The total mechanical energy of the system containing only the block increases from the moment of release to the moment it strikes the ground. D) The total mechanical energy of the block-Earth system remains constant.

C) The total mechanical energy of the system containing only the block increases from the moment of release to the moment it strikes the ground. D) The total mechanical energy of the block-Earth system remains constant.

A 1.0 kg lump of clay is sliding to the right on a frictionless surface with speed 2 m/s . It collides head-on and sticks to a 0.5 kg metal sphere that is sliding to the left with speed 4 m/s . What is the kinetic energy of the combined objects after the collision? A) 6 J B) 4 J C) 2 J D) 0 J

D) 0 J

A planet with half Earth's mass and half Earth's radius is discovered. What would an astronaut who weighs 800 N on Earth weigh on the planet? A) 100 N B) 200 N C) 400 N D) 800 N E) 1600 N

D) 1600 N

The figure shows the net force exerted on the satellite by the moon and the direction of the tangential velocity of the satellite at time t0. Which of the following statements is true regarding the motion of the satellite? A) The gravitational force exerted on the satellite by the moon will increase after time t0. B) The satellite accelerates in a direction that is parallel to the direction of the tangential velocity. C) The satellite will move toward the moon after time t0. D) The tangential velocity of the satellite does not remain constant.

D) The tangential velocity of the satellite does not remain constant.

A block on a horizontal surface of negligible friction is placed in contact with an ideal spring, as shown above. The block is moved to the left so that the spring is compressed a distance x from equilibrium and then released from rest. The block has kinetic energy K1 when it separates from the spring. When the spring is compressed a distance 2x and the block is released from rest, the kinetic energy of the block when it separates from the spring is A) K1/2 B) K1 C) √2K1 D) 2K1 E) 4K1

E) 4K1

A satellite is a large distance from a planet, and the gravitational force from the planet is the only significant force exerted on the satellite. The satellite begins falling toward the planet, eventually colliding with the surface of the planet. As the satellite falls, which of the following claims is correct about how the force that the planet exerts on the satellite Fps changes and how the force that the satellite exerts on the planet Fsp changes, if at all? What reasoning supports this claim?

Fps and Fsp both increase. The gravitational forces that two objects exert on one another decrease as the separation between the objects increases, and these forces are always equal in magnitude.

A rocket is continuously firing its engines as it accelerates away from Earth. For the first kilometer of its ascent, the mass of fuel ejected is small compared to the mass of the rocket. For this distance, which of the following indicates the changes, if any, in the kinetic energy of the rocket, the gravitational potential energy of the Earth-rocket system, and the mechanical energy of the Earth-rocket system?

Rocket Kinetic Energy: Increasing System Gravitational Potential Energy: Increasing System Mechanical Energy: Increasing

A student conducts an experiment in which a 0.5 kg ball is spun in a vertical circle from a string of length 1 m, as shown in the figure. The student uses the following equation to predict the force of tension exerted on the ball whenever it reaches the lowest point of its circular path at a known tangential speed for various trials. When the experiment is conducted, the student uses a force probe to measure the actual force of tension exerted on the ball. Why is the predicted force of tension different than the actual force of tension?

The student did not account for the downward force due to gravity at the ball's lowest point along its circular path, so the predicted force of tension is the net centripetal force exerted on the ball.

An object is thrown upward with a speed of 20m/s near the surface of a planet where the gravitational field strength is a constant magnitude of 6N/kg. The vertical position versus time of the object is shown in the graph. Is the object considered to be in free fall?

Yes, because the only force exerted on the object is the force due to gravity from the planet.

A railroad car of mass m is moving with speed u when it collides with and connects to a second railroad car of mass 3m, initially at rest, as shown above. How do the speed and kinetic energy of the connected cars compare to those of the single car of mass m before the collision?

A) Speed: Less Kinetic Energy: Less

A moon orbits an isolated planet in deep space. Which of the following forces that the planet exerts on the moon can be considered as negligible? A) The electric force B) The force due to gravity C) Both the electric force and the force due to gravity D) Neither the electric force nor the force due to gravity

A) The electric force

An object is released from rest at a height H near and above the surface of Earth. As the object falls toward the surface, Earth's atmosphere exerts a resistive force on the object such that it reaches a terminal velocity before it reaches the ground. Which of the following claims is true? Select two answers. A) The system consisting of only the object is an open system. B) Earth's atmosphere does negative work on the object as it falls toward the surface. C) The change in the object's kinetic energy from the instant it is released from rest, to the instant it reaches terminal velocity, is zero. D) The total mechanical energy of the object-Earth system remains constant at all times in which the object is in motion.

A) The system consisting of only the object is an open system. B) Earth's atmosphere does negative work on the object as it falls toward the surface.

A pendulum has a length l and a bob of mass m. Which of the following is true of the linear momentum of the bob as it swings from its highest to lowest point? A) It remains constant because momentum is always conserved. B) It increases in magnitude and changes direction. C) It decreases in magnitude and does not change direction. D) It is converted to angular momentum. E) It is converted to kinetic energy.

B) It increases in magnitude and changes direction.

A satellite of mass m orbits a moon of mass M in uniform circular motion with a constant tangential speed of v. The satellite orbits at a distance R from the center of the moon. Which of the following is a correct expression for the time T it takes the satellite to make one complete revolution around the moon?

B) T=2π√R^3/GM

A block of mass M is at rest on a ramp that is inclined at an angle θ with respect to the horizontal. Frictional forces are considered to be nonnegligible. The block is pushed against a spring and then held in place. The spring is compressed a distance of x1, and the spring is not secured to the block. The block is then released from rest, travels up the incline, and comes to rest after traveling a distance D, as shown above. Which of the following claims correctly describes the energy of the system under consideration from when the block compressed the spring and when the block has traveled a distance D along the incline? Select two answers. A) The mechanical energy of the system consisting of the spring increases by 1/2kx2 B) The mechanical energy of the system consisting of the block does not change. C) The mechanical energy of the system consisting of the block and Earth increases by more than zero but less than 1/2kx2 D) The mechanical energy of the system consisting of the spring, block, and Earth increases by 1/2kx2

B) The mechanical energy of the system consisting of the block does not change. C) The mechanical energy of the system consisting of the block and Earth increases by more than zero but less than 1/2kx2

A spacecraft is placed in a circular orbit around a planet with mass 6.4 x 1023 kg. The spacecraft orbits at a height of 4.5 x 107 m above the planet's surface. What additional information is needed to calculate the speed of the spacecraft in the orbit? A) No additional information B) The planet's radius only C) The spacecraft's mass only D) Both the planet's radius and the spacecraft's mass

B) The planet's radius only

Block X slides along a horizontal surface with a speed vX toward block Y that is initially at rest, as shown in Figure 1. After block X collides with block Y, the two blocks remain stuck together and travel at a velocity of vXY, as shown in Figure 2. Frictional forces are considered to be negligible. Which of the following claims is correct regarding the momentum of the system containing only block X and the system that contains block X and block Y? A) The system containing block XX is an open system, and the system of both blocks is an open system. B) The system containing block XX is an open system, and the system of both blocks is a closed system. C) The system containing block XX is a closed system, and the system of both blocks is an open system. D) The system containing block XX is a closed system, and the system of both blocks is a closed system.

B) The system containing block XX is an open system, and the system of both blocks is a closed system.

Two objects of the same mass travel in the same direction along a horizontal surface. Object X has a speed of 5 ms and object Y has a speed of 2 ms, as shown in the figure. After a period of time, object X collides with object Y. Consider the situation in which the objects collide but do not stick together. Which of the following predictions is true about the center of mass of the two-object system immediately after the collision? A) The center of mass does not move. B) The velocity of the center of mass does not change. C) The velocity of the center of mass decreases in speed. D) The velocity of the center of mass increases in speed.

B) The velocity of the center of mass does not change.

A rocket lifts a payload upward from the surface of Earth. The radius of Earth is R, and the weight of the payload on the surface of Earth is W. The force of Earth's gravity on the payload is W2 when the rocket's distance from the center of Earth is A) R B) √2R C) 2R D) 2√2R E) 4R

B) √2R

A person holds a book at rest a few feet above a table. The person then lowers the book at a slow constant speed and places it on the table. Which of the following accurately describes the change in the total mechanical energy of the Earth-book system? A) The total mechanical energy is unchanged, because there is no change in the book's kinetic energy as it is lowered to the table. B) The total mechanical energy is unchanged, because no work is done on the Earth-book system while the book is lowered. C) The total mechanical energy decreases, because the person does positive work on the book by exerting a force that opposes the gravitational force. D) The total mechanical energy decreases, because the person does negative work on the book by exerting a force on the book in the direction opposite to its displacement.

D) The total mechanical energy decreases, because the person does negative work on the book by exerting a force on the book in the direction opposite to its displacement.

A block of known mass M is at rest at the base of a ramp. A second identical block of mass M travels at a known, constant velocity v0, as shown in Figure 1. The block that travels at a constant speed collides with and sticks to the first block. Both blocks slide up the ramp and travel with an unknown velocity vR at the top of the ramp, as shown in Figure 2. All frictional forces are considered to be negligible. Which quantity should the student measure, if any, to determine whether the conservation of momentum applies to the two-block system from immediately before the collision to immediately after the blocks have reached the top of the ramp while stuck together? Justify your selection. A) The force due to gravity exerted on both blocks as they travel up the ramp, because the force due to gravity does work on the system as it travels up the ramp. B) The time in which the blocks travel up the ramp, because this can be used to determine the change in momentum of the system from before the collision to after the collision. C) The acceleration of both blocks as they travel up the ramp, because this can be used to determine the average net force exerted on the blocks. D) The velocity vR of the two-block system at the top of the ramp, because this can be used to determine the final momentum of the system.

D) The velocity vR of the two-block system at the top of the ramp, because this can be used to determine the final momentum of the system.

How does an air mattress protect a stunt person landing on the ground after a stunt? A)It reduces the kinetic energy loss of the stunt person. B) It reduces the momentum change of the stunt person. C) It increases the momentum change of the stunt person. D) It shortens the stopping time of the stunt person and increases the force applied during the landing. E) It lengthens the stopping time of the stunt person and reduces the force applied during the landing.

E) It lengthens the stopping time of the stunt person and reduces the force applied during the landing.