Ch.3 Work and Machines

For work to be done on an object

• some force need only be exerted on the object

• the object must move some distance as a result of a force

• the must move, whether or not a force is exerted on it

• the object must not move

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If you exert a force of 20 newtons (N) to push a desk 10 meters (m), how much work do you do on the desk?

• 200 joules

• 30 joules

• 10 joules

• 100 joules

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The mechanical advantage of a machine is the number of times a machine increases

• the distance an object is moved

• the amount of friction

• the change in direction

• the force exerted on the machine

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A simple machine that might be thought of as an inclined plane that moves is a

• lever

• wheel and axle

• wedge

• pulley

One example of a compound machine is a

• door

• pliers

• bicycle

• shovel

The ideal mechanical advantage for an inclined plane is equal to the length of the incline divided by the

• mass of the incline

• slope of the incline

• height of the incline

• angle of the incline

How can a hockey stick be considered a machine?

• it increases force

• it multiplies distance

• it changes direction

• it reduces friction

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If tight scissors have an efficiency of 50 percent, half of your work is wasted due to

• the output force

• the input force

• friction

• changes in direction

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Power is measured in units called

• joules

• pounds

• watts

• newtons

The wedge, screw, and lever are all

• simple machines

• compound machines

• found in the human body

• 100 percent efficient