chapter 7

How much power is required to raise a 200-kg crate a vertical distance of 2 m in a time of 4 s?

1000 W

In an ideal pulley system, a woman lifts an 80-N crate by pulling a rope downward with a force of 20 N. For every 1-meter length of rope she pulls downward, the crate rises

25 cm

When you do 1000 J of work on a car jack and the gravitational potential energy of the car is increased by 300 J, the efficiency of the jack is

30%

When two identical cars, one traveling twice as fast as the other, brake to a stop using old-fashioned brakes, the faster car will skid

4 times as far.

A model airplane moves twice as fast as another identical model airplane. Compared with the kinetic energy of the slower airplane, the kinetic energy of the faster airplane is

4 times as much.

An empty truck traveling at 10 km/h has kinetic energy. How much kinetic energy does it have when its speed is doubled?

4 times the KE

How much work is done on a 200-kg crate that is hoisted 2 m in a time of 4 s?

4000 J

A shiny sports car at the top of a vertical cliff has a potential energy of 100 MJ relative to the ground below. Unfortunately, a mishap occurs and it falls over the edge. When it is halfway to the ground, its kinetic energy is

50 MJ.

Which of the following equations is most directly useful for solving a problem that asks for the distance a speeding vehicle skids in coming to a stop?

Fd = ∆(1/2 mv2)

A simple machine CANNOT multiply

energy

Which of these forms of energy is NOT renewable?

fossil-fuel power

When a car is braked to a stop, unless it is a hybrid, its kinetic energy is transformed to

heat

If a charging elephant has kinetic energy, it must also have

momentum.

A model airplane moves 3 times as fast as another identical model airplane. Compared with the kinetic energy of the slower airplane, the kinetic energy of the faster airplane is

more than 4 times as much.

When an increase in speed doubles the momentum of a moving body, its kinetic energy

more than doubles

A dog and a mouse run down the road with the same KE. The faster moving one is the

mouse

A pendulum bob swings to and fro. Its kinetic energy and its potential energy relative to the bottom of its swing are the same at

one-half the vertical distance between the bottom and the top of the swing.

When work is done twice as quickly, then the power expended is

twice

A 1-kg ball has twice the speed as a 2-kg ball. Compared with the 1-kg ball, the 2-kg ball has

twice the kinetic energy.

The most energy per unit mass can be extracted from

uranium.