PHY031-OQuiz-M01-W04-01

A donkey pulls a crate up a rough, inclined plane at constant speed. Which one of the following statements concerning this situation is false?

• The gravitational potential energy of the crate is increasing.

• The net work done by all the forces acting on the crate is zero joules.

• The work done on the crate by the normal force of the plane is zero joules.

• The donkey does "positive" work in pulling the crate up the incline.

• The work done on the object by gravity is zero joules.

A mountain climber pulls a supply pack up the side of a mountain at constant speed. Which one of the following statements concerning this situation is false?

• The net work done by all the forces acting on the pack is zero joules.

• The work done on the pack by the normal force of the mountain is zero joules.

• The work done on the pack by gravity is zero joules.

• The gravitational potential energy of the pack is increasing.

• The climber does "positive" work in pulling the pack up the mountain.

After an ice storm, ice falls from one of the top floors of a 65-story building. The ice falls freely under the influence of gravity. Which one of the following statements concerning this situation is true? Ignore any effects due to non-conservative forces.

• The kinetic energy of the ice increases by equal amounts for equal distances.

• The kinetic energy of the ice increases by equal amounts for equal times.

• The potential energy of the ice decreases by equal amounts for equal times.

• The total energy of the block increases by equal amounts over equal distances.

• As the block falls, the net work done by all of the forces acting on the ice is zero joules.

Two balls of equal size are dropped from the same height from the roof of a building. One ball has twice the mass of the other. When the balls reach the ground, how do the kinetic energies of the two balls compare?

• The lighter one has one fourth as much kinetic energy as the other does.

• The lighter one has one half as much kinetic energy as the other does.

• The lighter one has the same kinetic energy as the other does.

• The lighter one has twice as much kinetic energy as the other does.

• The lighter one has four times as much kinetic energy as the other does.

Two identical balls are thrown from the same height from the roof of a building. One ball is thrown upward with an initial speed v. The second ball is thrown downward with the same initial speed v. When the balls reach the ground, how do the kinetic energies of the two balls compare? Ignore any air resistance effects.

• The kinetic energies of the two balls will be the same.

• The first ball will have twice the kinetic energy as the second ball.

• The first ball will have one half the kinetic energy as the second ball.

• The first ball will have four times the kinetic energy as the second ball.

• The first ball will have three times the kinetic energy as the second ball.

What is the relationship between the gravitational potential energy of an object and the work done on the object by the gravitational force?

• The work is equal to the gravitational potential energy.

• The negative of the work is equal to the change in the gravitational potential energy.

• The negative of the work is equal to the square of the gravitational potential energy.

• The work is equal to the square of the gravitational potential energy.

Complete the following statement:

A force that acts on an object is said to be conservative if

• the work it does on the object is equal to the increase in the object's kinetic energy

• the work it does on the object is independent of the path of the motion.

• it always acts in the direction of motion of the object.

• it results in a change in the object's kinetic energy.

A ball is constrained to follow a circular path by a conservative force.  During a time interval t, the ball makes exactly one revolution.  Which one of the following statements concerning the net work done on the ball during time t is true?

• The net work depends only on the time t.

• The net work depends only on the velocity of the ball.

• The net work depends only on the radius of the circle.

• The net work is equal to zero joules.

A ball is thrown vertically upward in the air.  Which one of the following quantities is necessarily equal to zero at the highest point of the ball’s trajectory?

• acceleration

• net force

• potential energy

• kinetic energy

Complete the following statement:

The total energy of a system can only change

• if the forces acting in the system are nonconservative.

• if there are no external forces acting on the system.

• if the forces acting in the system are conservative.

• by transferring amounts of energy to or from the system.