Physical Science - Homework 5

A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is

10 %

It takes 40 J to push a large crate 4 m across a floor. The force exerted on the crate is

10 N

A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has

16 times the KE

A car moving at 50 km/hr skids 20 m with locked brakes. How far will the car skid with locked brakes if it's initial speed is 150 km/hr?

180 m

Exert 100 J in 50 seconds and your power output is

2 W

A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its height?

2 m

When the input piston of a hydraulic press is depressed 20 cm, the output piston is observed to move 1 cm. An input force of 1 N can raise no more than

20 N

A bow is drawn so that it has 40 J of potential energy. When the arrow is fired, it's kinetic energy is ideally

40 J

A music console is pushed a distance of 2 m with a force of 20 N. The work done on the console is

40 J

In raising a 5000 N piano with a pulley system, for every 1 m of rope pulled down, the piano rises 0.1 m. Ideally, this means the force needed to lift the piano is

500 N

A 2-kg mass weighs 20 N and is held 4 m above the ground. Its potential energy relative to the ground is

80 J

True or false: Strictly speaking, if any electrical device in an automobile is turned on (such as an air conditioner, headlights or radio), more fuel is consumed by the engine.

True

Which requires more work: lifting a 50 kg sack vertically 2 m or lifting a 25 kg wack vertically 4 m?

both require the same amount of work

When a simple machine multiples force, it decreases

distance moved

The following equation e = useful energy output/total energy input is used to solve:

efficiency

True or false: A hydraulic press properly arranged, like a simple lever, is capable of multiplying energy input.

false

The following equation F = w/d is used to solve for:

force

A clerk can lift containers a vertical distance of 1 m, or roll them up a 2 m long ramp to the same elevation. With the ramp, the applied force needed is

half as much

When a non-hybrid car brakes to a stop its kinetic energy transforms to

heat

Compared to a recoiling rifle, the bullet that is fired has a greater

kinetic energy

If a charging rhinoceros has momentum, it must also have

kinetic energy

The following equation KE = 1/2•m•v^2 is used to solve:

kinetic energy

An object may have PE because of its

location

How much work does the force of gravity do on a 30 lb bowling ball rolling down a 20 ft lane?

none because the force acts perpendicular to the distance traveled

The following equation PE = mgh is used to solve for

potential energy

The following equation p = work/time is used to solve:

power

Which has greater kinetic energy, a car traveling at 30 km/h or another car of half the mass traveling at 60 km/h?

the 60 km/h car

The most fundamental feature of machines is

the conservation of energy

If you do work on an object in half the time, your power output is

twice

An object lifted 10 m gains a certain amount of PE. If it's lifted 20 m, it's gain in PE is

twice as much

If you push an object twice as far while applying the same force, you do

twice as much as work

The following equation w = F • d is used to solve for:

work