Work & Energy

A person carries a 2.50-N pebble through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 405s. How much work did gravity do on the rock between A and B?

• 45 J

• -45 J

• 37.5 J

• -37.5 J

A person carries a 2.50-N pebble through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 405s. How much work did the person do on the rock between A and B?

• 45 J

• -45 J

• 37.5 J

• -37.5 J

Linda does four times as much work as James does and in one-third the time. Linda’s power output is ________.

• four times James’ power output

• the same as James’ power output

• twelve times James’ power output

• cannot be determined

Work is ____.

• a scalar

• a vector

• neither a scalar nor vector

• both a scalar and vector

What is the kinetic energy of a 50 N boulder resting at the top of a 25 m cliff?

• 1250 J

• 625 J

• 0 J

• 12500 J

Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. If there is no air resistance, when they hit the ground _______.

• the heavier one will have half the kinetic energy of the lighter one

• the heavier one will have twice the kinetic energy of the lighter one

• the heavier one will have one-fourth the kinetic energy of the lighter one

• the heavier one will have four times the kinetic energy of the lighter one

Three cars (car A, car B, and car C) are moving with the same speed when the drivers slam on their brakes. The most massive car is car A, and the least massive is car C. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, for which car is the amount of work done by friction in stopping it the greatest?

• The amount of work done by friction is the same for all cars.

• Car A

• Car B

• Car C

The graph plots velocity against time. During which interval is no work done?

• Between A & B

• Between B & C

• Between C & D

• Between D & E

The graph plots velocity against time. What feature of the graph shows negative work?

• Velocity increases

• Velocity remains constant

• Velocity decreases

• Cannot be determined

Constant velocity implies

• a = 0 m/s²

• Fnet = 0 N

• Balanced forces

• W = 0 J

• All of the above