Physics exam 3

What is the kinetic energy of a satellite of mass m that orbits the Earth, of mass M, in a circular orbit of radius R?

(½ GMm)/R

If the block experiences a constant friction force of 10 N, how much work is done by the friction force?

-50 J

The figures above show a small block of mass 0.20 kg on a track in the shape of a circular arc. The block is released from rest at a height H above the floor, as shown in Figure 1. The block slides along the track with negligible friction and leaves it at a height of 0.40 m above the floor and a speed of 3.0 m/s at a 30o angle, as shown in Figure 2. The height H is most nearly

0.86 m

Two identical balls have initial velocities v1 = 4 m/s to the right and v2 = 3 m/s to the left, respectively. The balls collide head on and stick together. What is the velocity of the combined balls after the collision?

1/2 m/s to the right

A ball of mass 0.4 kg is initially at rest on the ground. It is kicked and leaves the kicker's foot with a speed of 5.0 m/s in a direction 60o above the horizontal. The magnitude of the impulse imparted by the ball to the foot is most nearly

2 N • s

Two balls, of mass m and 2m, collide and stick together. The combined balls are at rest after the collision. If the ball of mass m was moving 5 m/s to the right before the collision, what was the velocity of the ball of mass 2m before the collision?

2.5 m/s to the left

A block of weight mg = 100 N slides a distance of 5.0 m down a 30-degree incline, as shown above. How much work is done on the block by gravity?

250 J

A mass m is attached to a mass 3m by a rigid bar of negligible mass and length L. Initially, the smaller mass is located directly above the larger mass, as shown above. How much work is necessary to flip the rod 180° so that the larger mass is directly above the smaller mass?

2mgL

Two identical balls of mass m = 1.0 kg are moving towards each other, as shown above. What is the initial kinetic energy of the system consisting of the two balls?

36 joules

A car slows down on a highway. Its engine is providing a forward force of 1000 N; the force of friction is 3000 N. It takes 20 s for the car to come to rest. What is the car's change in momentum during these 20 s?

40,000 kg . m/s

A 0.30-kg bird is flying from right to left at 30 m/s. The bird collides with and sticks to a 0.50-kg ball which is moving straight up with speed 6.0 m/s. What is the magnitude of the momentum of the ball/bird combination immediately after collision?

9.5 N • S

A block is given a short push then slides with constant friction across a horizontal floor. The graph above shows the kinetic energy of the block after the push ends as a function of an unidentified quantity. The quantity could be which of the following? Select two answers

B. Distance traveled by the block D. Magnitude of the network done on the block

A 0.2 kg rock is dropped into a lake from a few meters above the surface of the water. The rock reaches terminal velocity in the lake after 5 s in the water. During the final 3 s of its descent to the lake bottom, the rock moves at a constant speed of 4 m/s. Which of the following can be determined from the information given? Select two answers.

C. The acceleration of the rock 2 s before it reaches the lake bottom D. The change in potential energy of the rock-Earth-water system during the final 3 s of the rock's descent

Three objects can only move along a straight, level path. The graphs below show the position d of each of the objects plotted as a function of time t. The magnitude of the momentum of the object is increasing in which of the cases.

III only

Two objects having the same mass travel toward each other on a flat surface, each with a speed of 1.0 m/s relative to the surface. The objects collide head-on and are reported to rebound after the collision, each with a speed of 2.0 m/s relative to the surface. Which of the following assessments of this report is most accurate?

If potential energy was released to the objects during the collision, the report could be true.

Block B is at rest on a smooth tabletop. It is attached to a long spring, which in turn is anchored to the wall. Block A slides toward and collides with block B. Consider two possible collisions: Case I: Block A bounces back off of block B. Case II: Block A sticks to block B. 3. Which of the following is correct about the speed of block B immediately after the collision?

It is faster in case I than in case II regardless of the mass of each block.

In the setup shown above, a student uses motion detector 1 to measure the speed vi of a cart with mass m before it collides with and sticks to a stationary cart with mass M. Motion detector 2 measures the speed vf of the carts after the collision. The student repeats the experiment several times using different values of vi and creates a graph of vf as a function of vi. The slope of this graph is most nearly equal to

M/(M + m)

A person exerts an upward force on a box, as shown above. The box may be moving upward, downward, or not at all while the person exerts the upward force. For which of the following motions of the box is the work down by the person on the box correctly indicated?

Motion of the box: Downward with increasing speed Work done by person on box: Negative

A block is held at rest against a compressed spring at point A at the top of a frictionless track of height h, as shown above. The block is released, loses contact with the spring at point B, and slides along the track until it passes point C, also at height h. How do the potential energy U of the block-Earth system and the kinetic energy K of the block at point C compare with those at point A?

Potential energy of block-earth system: UC = UA Kinetic energy of block: KC > KA

An open cart on a level surf ace is rolling without frictional loss through a vertical downpour of rain as shown above. As the cart rolls, an appreciable amount of rainwater accumulates in the cart. The speed of the cart will

decrease because of conservation of momentum.

A ball collides with a stationary block on a frictionless surface. The ball sticks to the block. Which of the following would NOT increase the force acting on the ball during the collision?

increasing the time it takes the ball to change the block's speed

A child pushes horizontally on a box of mass m which moves with constant speed v across a horizontal floor. The coefficient of friction between the box and the floor is µ. At what rate does the child do work on the box?

µmgv

Objects X and Y are constrained to move along a straight line. The graphs above show the net force exerted along that line on each of the object as functions of time. Which of the following correctly ranks the change in momentum ∆p of the objects?

∆px = ∆py

A stationary object explodes, breaking into three pieces of masses m, m, and 3m. The two pieces of mass m move off at right angles to each other with the same magnitude of momentum mV, as shown in the diagram above. What are the magnitude and direction of the velocity of the piece having mass 3m?

√(2)/3 V (vector is left and down)

A ball rolls horizontally with speed v off of a table a height h above the ground. Just before the ball hits the ground, what is its speed?

√(v 2 + 2gh)