Chapter 8 Semester Test

In physics, work is defined as...

force times distance.

If you lift two loads up one story, how much work do you do compared to lifting just one load up one story?

twice as much.

The unit of work is the...

joule.

Power is defined as the...

work done on an object divided by the time taken to do the work.

The unit of power is the...

watt.

Potential energy is the energy an object has because of its...

location.

The amount of potential energy possessed by an elevated object is equal to...

the work done in lifting it.

Kinetic energy of an object is equal to...

one half the product of its mass times its speed squared.

An arrow in a bow has 70-J of potential energy. Assuming no loss of energy to heat, how much kinetic energy will it have after it has been shot...

70-J.

When a car's speed tripples, its kinetic energy..

increases by nine times.

A job is done slowly, and an identical job is one quickly. Both jobs require the same amount of work but different amounts of...

power.

Which requires more work: lifting a 70-kg sack vertically 2 meters or lifting a 35-kg sack vertically 4 meters?

Both require the same amount of work.

A ball is thrown into the air with 100-J of kinetic energy, which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is...

less than 100-J.

An object that has kinetic energy mush be...

moving.

An object that has kinetic energy mush have...

momentum.

Which has greater kinetic energy, a car traveling at 30 km/h or a half-as-massive car traveling at 60 km/h?

The 60 km/h car.

An object at rest may have...

energy.

All simple machines ideally work on the principle that...

work input equals work output.

The ratio of output force to input force of a simple machine is called the...

mechanical advantage.

A pulley system can...

Change teh direction of a force.
Multiply the force.

The ratio of useful work output to total work input is called the...

efficiency.

It takes 80-J to push a large box 8-m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box?

10-N

Sue can easily lift a 45.o-N rock with the help of a lever. When she pushes down with 20.0-N force, she lifts the rock 0.3 meters. How far does she move her arms to do this?

0.7-M

A certain jack has a theoretical mechanical advantage of 300. However, due to frictional forces, the actual mechanical advantage is only 100. What is the efficiency of the jack?

1/3

Blackie, a cat whose mass is 5.45-kg, is napping on top of the refrigerator when he rolls over and falls. Blackie has a KE of 85.5-J just before he lands on his feet on the floor. How tall is the refrigerator?

___=____=

Mr. Mac, a computer technician, uses a screwdriver with a handle of radius 1.2-cm to remmove a screw in the back of a computer. The screw moves out 0.20-cm on each complete turn. What is the ideal mechanical advantage of the screwdriver?

0