chapter 8

In which one of the following systems is there an increase in gravitational potential energy? a. A child accidentally releases a helium-filled balloon and it flies upward toward the clouds. b. My cat Yadi patiently waits on the floor by his food bowl for dinner. c. My cat Yadi jumps down from a bed and lands on his feet. d. A truck drives at an average velocity of 25 m/s, due north along a level, county road.

a. A child accidentally releases a helium-filled balloon and it flies upward toward the clouds

Block 1 and block 2 have the same mass, m, and are released from the top of two inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. If the coefficient of friction is the same in both cases, which of the blocks is going faster when it reaches the bottom of its respective incline? a. Block 2 is faster. b. We must know the actual masses of the blocks to answer. c. Block 1 is faster. d. Both blocks have the same speed at the bottom.

a. Block 2 is faster.

Two blocks of masses m1 and m2 are released from the top of two frictionless inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. Which of the blocks is going faster when it reaches the bottom of its respective incline? a. Both blocks have the same speed at the bottom. b. We must know the actual masses of the blocks to answer. c. Block 1 is faster. d. Block 2 is faster

a. Both blocks have the same speed at the bottom.

An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U. a. K increases and U decreases. b. K decreases and U decreases. c. K increases and U increases. d. K decreases and U increases.

a. K increases and U decreases.

A mass is attached to one end of a string. The other end of the string is attached to a rigid support. The mass is released at A and swings in a vertical arc to points B, C, and D, as shown in Figure 8-3. Neglect air resistance. At what point does the mass have the least potential energy? a. B b. C c. A d. D

b. C

Which of the following is false regarding energy? a. Energy is conserved. b. Energy can be created. c. Energy can be transferred. d. Energy can be transformed.

b. Energy can be created.

Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare? a. The maximum height of the second ball is 1.41 times that of the first ball. b. The maximum height of the second ball is four times that of the first ball. c. The maximum heights of the two balls are equal. d. The maximum height of the second ball is two times that of the first ball.

b. The maximum height of the second ball is four times that of the first ball.

A mass is attached to one end of a string. The other end of the string is attached to a rigid support. The mass is released at A and swings in a vertical arc to points B, C, and D, as shown in Figure 8-3. Neglect air resistance. At what point does the mass have the most kinetic energy? a. B b. A c. C d. D

c. C

If the slope of the curve on a potential energy versus position graph is positive, what can we say about the force? a. Force cannot be determined from a potential energy vs. position graph. b. The force is zero. c. The force is negative. d. The force is positive

c. The force is negative.

Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height? a. Object 1 rises to the greater height because it possesses a smaller amount of kinetic energy. b. Object 2 rises to the greater height because it contains more mass. c. The two objects rise to the same height. d. Object 2 rises to the greater height because it possesses a larger amount of kinetic energy.

c. The two objects rise to the same height.

The total mechanical energy of a system a. is equally divided between kinetic energy and potential energy. b. is either all kinetic energy or all potential energy, at any one instant. c. is constant, only if conservative forces act. d. can never be negative.

c. is constant, only if conservative forces acts

A block of mass m slides without friction on a table with speed v. It hits and compresses a spring of force constant k by a distance l. The spring then expands again ejecting the block in the opposite direction as it was originally traveling. Neglecting the mass of the spring, what is the speed of the object after it is ejected by the spring? a. 2v b. v/2 c. v d. 4v

c. v

You and your friend want to go to the top of the Empire State Building. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy (U) of you and your friend, after you both reach the top. Assume you have the same mass. a. Your friend's U is greater than your U, because she got to the top faster. b. It is impossible to tell, since the times are unknown. c. It is impossible to tell, since the distances are unknown. d. Both of you have the same amount of potential energy.

d. Both of you have the same amount of potential energy.

Which of the following statements is true? a. A conservative force permits a two-way conversion between kinetic and potential energies. b. A potential energy function can be specified for a nonconservative force. c. The work done by a conservative force depends on the path taken. d. all of these

d. all of these

Complete the following statement: A force that acts on an object is said to be conservative if a. if the work it does on a closed path is zero. b. the work it does can be stored in a form of energy that can be released later. c. the work it does on the object is independent of the path of the motion. d. all of these

d. all of these.