Physics Questions Study guide

Two carts, of mass 2 m and m, approach each other head-on with the same speed v, as shown in the figure above. When the carts collide, they hook together. Assuming positive momentum is to the right, which of the following best represents the momentum of the cart of mass m as a function of time before and after the collision?

C

In which of the following situations is the kinetic energy of the object decreasing?

C

A 2 kg object traveling at 5 m/s on a frictionless horizontal surface collides head-on with and sticks to a 3 kg object initially at rest. Which of the following correctly identifies the change in total kinetic energy and the resulting speed of the objects after the collision?

C

A system consists of two spheres, of mass m and 2 m, connected by a rod of negligible mass, as shown above. The system is held at its center of mass with the rod horizontal and released from rest near Earth's surface at time t = 0. The graph above shows the rate of change of linear momentum of the sphere of mass m as a function of time. What is the linear momentum of the two-sphere system at time t = 3.0 s ?

B ?

A block is held at rest against a wall by a force of magnitude F exerted at an angle θ from the horizontal, as shown in the figure above. Let Fg be the gravitational force exerted by Earth on the block, Fn be the normal force exerted by the wall on the block, and Ff be the frictional force exerted by the wall on the block. Which of the following statements about the magnitudes of the forces on the block must be true? Select two answers.

B and C

Object A has mass 2 kg and is traveling to the right at speed 3 m/s. Object B is traveling to the left at 3 m/s. The objects collide head-on, and afterward each has a speed of 3 m/s. Which of the following could be the mass of object B? Select two answers.

B and D

A box of mass m is on a rough inclined plane that is at an angle θ with the horizontal. A force of magnitude F t an angle Φ with the plane is exerted on the block, as shown above. As the block moves up the plane, there is a frictional force between the box and the plane of magnitude f. What is the magnitude of the net force acting on the box?

C

A cart of known mass moves with known speed along a level, friction less track, as shown in the figure above. The cart hits a force sensor and rebounds. The force sensor measures the force exerted on the cart as a function of time and as a function of the position of the cart. The results will be graphed on the axes shown. Which of the two graphs can be used to determine the cart's speed after it rebounds?

C

A child slides from rest down slides A and B shown above. The slides are the same height, and the coefficient of friction between the slides and the child is the same. Which f the following compares the change ΔK in the kinetic energy of the child and the change ΔU in the potential energy of the child-Earth system for the two slides?

C

For another identical object initially at rest, no frictional force is exerted during segment 2 (between t = 2 s and t = 4 s). A rope exerts the same constant force of magnitude F T as in the previous scenario. What is the change in the object's kinetic energy during segment 2?

C

The graph above shows velocity v as a function of time t for a 0.50 kg object traveling along a straight line. The graph has three segments labeled 1, 2, and 3. A rope exerts a constant force of magnitude FT on the object along its direction of motion the whole time. During segment 2 only, a frictional force of magnitude Ff is also exerted on the object. Which of the following expressions correctly relates the magnitudes Ff and FT?

C

The stacks of boxes shown in the figure above are inside an elevator that is moving upward. The masses of the boxes are given in terms of the mass M of the lightest box. Assume the elevator is moving at a constant speed, and consider the bottom box in the stack that has two boxes of mass 2 M. Let F floor be the force exerted by gravity on the box, and F box be the force exerted by the top box on the bottom box. Which of the following best represents the forces exerted on the bottom box?

C

Three identical blocks each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a friction less incline. Block c is projected horizontally with an initial speed v. Which block has the greatest speed just before hitting the ground?

C

An object is moving to the right with speed vi when a force of magnitude F is exerted on it. In which of the following situations is the object's direction of motion changing and kinetic energy decreasing at the instant shown?

D

An object is moving to the west at a constant speed. Three forces are exerted on the object. One force is 10 N directed due north, and another is 10 N directed due west. What is the magnitude and direction of the third force if the object is to continue moving to the west at a constant speed?

D

An object starts from rest and slides with negligible friction down an air track tipped at an angle θ from the horizontal. A student records values of the object's position along the track at various times. The value of θ can best be determined from which of the following?

D

Block A and block B move toward each other on a level friction less track. Block A has mass m and velocity +v. Block B has mass 2 m and velocity -v. The blocks collide and during the collision the magnitude of the net force exerted on block A is F. What is the magnitude of the net force exerted on block B, and why does it have that value?

D

Each of the figures above shows a tractor attached to an object. The tractor exerts the same constant force F on each object in every case. Which of the following is a true statement about an object and the relative magnitude of the force exerted by the object on the tractor?

D

In a one-dimensional perfectly elastic collision, an object of mass m is traveling with speed v o in the +x direction when it strikes an object with mass 3 m that is at rest. What are the objects' velocities following the collision?

D

Some students want to calculate the work done by friction as an object with unknown mass moves along a straight line on a rough horizontal surface. The students have a force probe, a meter stick, and a stopwatch. Which of the following will allow the students to take the measurements needed to calculate the work done by friction?

D

The graph above shows the position x as a function of time for the center of mass of a system of particles of total mass 6.0 kg. For a very short time interval around 2.0 s, an external force is exerted on an object in the system. What is the resulting change in momentum of the system?

D

Two objects, A and B, move toward one another. Object A has twice the mass and half of the speed of object B. Which of the following describes the forces the objects exert on each other when they collide and provides the best explanation?

D

Which of the following correctly ranks the displacement of Δx for the three segments of the objects motion?

D

Which of the following correctly ranks the displacement Δx for the three segments of the object's motion?

D

An athlete with mass m running at speed v grabs a light rope that hangs from a ceiling of height H and swings to a maximum height of h 1. In another room with a lower ceiling of height H/2, a second athlete with mass 2 m running at the same speed v grabs a light rope hanging from the ceiling and swings to a maximum height of h 2. How does the maximum height reached by the two athletes compare, and why?

D ?

Using a force probe, a student generates the graph above of the force exerted on a small wagon as a function of time. The wagon starts from rest and rolls with negligible friction in the axles. Which of the following graphs best represents the wagon's momentum as a function of time?

D ?

An elevator carrying a person of mass m is moving upward and slowing down. How does the magnitude F of the force exerted on the person by the elevator floor compare with the magnitude mg of the gravitational force?

A

A person is running on a track. Which of the following forces propels the runner forward?

C

A ball is dropped from rest and falls to the floor. The initial gravitational potential energy of the ball-Earth -floor system is 10 J. The ball then bounces back up to a height where the gravitational potential energy is 7 J. What was the mechanical energy of the ball-Earth-floor system the instant the ball left the floor?

??? (Not D) C?

A 50.0 N box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.50, and the coefficient of kinetic friction is 0.30. A horizontal 20.0 N force is then exerted on the box. The magnitude of the acceleration of the box is most nearlyfelev

A

A clay ball and a rubber ball of the same mass are moving toward a glider that is at rest on a friction less air track. The balls have the same speed, with the rubber ball moving toward the right and the clay ball moving toward the left, as shown above. The balls strike the glider at the same time. The clay ball sticks to the glider, and the rubber ball and bounces off it. Which of the following indicates the direction of motion of the glider after the collisions and explains why it moves in that direction?

A

A lion is running at constant speed toward a gazelle that is standing still, as shown in the top figure above. After several seconds, the gazelle notices the lion and accelerates directly toward him, hoping to pass the lion and force him to reverse direction. As the gazelle accelerates toward and past the lion, the lion changes direction and accelerates in pursuit of the gazelle. The lion and the gazelle eventually each reach constant but different speeds. Which of the following sets of graphs shows a reasonable representation of the velocities of the lion and gazelle as functions of time?

A

A person holds a 4.0 kg block at position A shown above on the left, in contact with an uncompressed vertical spring with a spring constant of 500 N/m. The person gently lowers the block from rest at position A to rest at position B. Which of the following describes the change in the energy of the block-spring-Earth system as a result of the block being lowered?

A

If the block is sliding up section 2, what is the magnitude of the force of friction that is exerted on the block by the incline?

A

A ball is suspended by a lightweight string, as shown in the figure above. The ball is displaced to position 1 and released. the four labeled positions are evenly spaced along the arc of the ball's motion. Between which adjacent pairs of positions is the change in kinetic energy of the ball greatest?

A ?

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 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?

B

A 50 kg athlete running at speed v grabs a light rope that hangs from a 10-meter-high platform and swings to a maximum of 1.8 m above the ground. Later, a 100 kg athlete, running at the same speed, grabs a similar rope hanging from a 5-meter-high platform. What is the maximum height to which the 100 kg athlete swings?

B

A block of mass 10 kg moves from position A to position B shown in the figure above. The speed of the block is 10 m/s at A and 4.0 m/s at B. The work done by friction on the block as it moves from A to b is most nearly

B

A kitten sits in a lightweight basket near the edge of a table. A person accidentally knocks the basket off the table. As the kitten and basket fall, the kitten rolls, turns, kicks, and catches the basket in its claws. The basket lands on the floor with the kitten safely inside. If air resistance is negligible, what is the acceleration of the kitten-basket system while the kitten and basket are in midair?

B

A spacecraft of mass 4000 kg is traveling in a straight line in the positive direction. Engines can be fired so that the force exerted on the spacecraft is in the positive or negative direction. The graph above shows data for the force during one interval. Which of the following is the best estimate of the net change in the speed of the spacecraft from time t = 0 to time t = 4 s ?

B

An object's velocity v as a function of time t is given in the graph above. Which of the following statements is true about the motion of the object?

B

As the crate slides a distance d, how does the new gain in kinetic energy compare to Δk?

B

Box A of mass m sits on the floor of an elevator, with box B of mass 2 m on top of it, as shown in the figure above. The elevator is moving upward and slowing down. FA is the magnitude of the force exerted on box A by box B, FB is the magnitude of the force exerted on box B by box A, and Fg is the magnitude of the gravitational force exerted on box B. Which of the following ranks the forces in order of increasing magnitude?

B

Does at least one of the ships have its engine turned on during the time interval shown, and what evidence indicates so?

B

Three identical blocks each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a friction less incline. Block C is projected horizontally with an initial speed v. Which block takes the longest time to reach the ground?

B

Three identical blocks each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a friction less incline. Block c is projected horizontally with an initial speed v. Which block takes the longest time to reach the ground?

B

A stone of mass m is thrown upward at a 30° angle to the horizontal. At the instant the stone reaches its highest point, why is the stone neither gaining nor losing speed?

C

To analyze the characteristics and performance of the brakes on a 1500 kg car, researchers collected the data shown in the table above. It shows the car's speed when the brakes are first applied and the corresponding braking distance required to stop the car. The magnitude of the average braking force on the car is most nearly

C

Two identical blocks are connected to the opposite ends of a compressed spring. The blocks initially slide together on a friction less surface with velocity v to the right. The spring is then released by remote control. At some later instant, the left block is moving at v/2 to the left, and the other block is moving to the right. What is the speed of the center of mass of the system at that instant?

C

Two identical carts are free to move along a straight friction less track. At time t 1, cart X is moving at 2.0 m/s when it collides with and sticks to cart Y, which is initially at rest. Which of the following graphs best shows the velocity of cart X before an after the collision?

C

Which of the following graphs best represents the net force f net exerted on the two-ship system?

C

A 1.0 kg lump of clay is sliding to the right on a friction less 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?

D

A blue sphere and a red sphere with the same diameter are released from rest at the top of a ramp. The red sphere takes a longer time to reach the bottom of the ramp. The spheres are then rolled off a horizontal table at the same time with the same speed and fall freely to the floor. Which sphere reaches the floor first?

D

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?

D

A small cart is rolling freely on an inclined ramp with a constant acceleration of 0.50 m/s^2 in the -x direction. At time t = 0, the cart has a velocity of 2.0 m/s in the +x direction. If the cart never leaves the ramp, which of the following statements correctly describes the motion of the cart at a time t > 5 s ?

D

A student is asked to determine the work done on a block of wood when the block is pulled horizontally using an attached string. The student is supplied with a spring scale, a stopwatch, and a meter stick. Which of the following graphical analysis techniques will allow the student to determine the work done on the block by the string?

D

An ice-skater is moving at a constant velocity across an icy pond. the skater throws a snowball directly ahead. Which of the following correctly describes the velocity of the center of mass of the skater-snowball system immediately after the snowball is thrown? Assume friction and air resistance are negligible.

D