Work and Machines

In which situation is a person doing work on an object?

• A school crossing guard raises a stop sign that weighs 10N.
• A student walks while wearing a backpack that weighs 15 N.
• A man exerts 350 N force on a rope attached to a house.
• A worker holds a box 1 m off the floor.

Which of the following simple machines were used by Egyptians to build pyramids?

• screws and screwdrivers
• inclined planes and levers
• plows and axes
• wheels and axles

If a barbell weighs 160 N, what other information do you need to calculate how much work it takes to lift it?

• the shape of the weights
• how high the barbell is being lifted
• the strength of the person doing the lifting
• the amount of output force

How does a ramp make lifting a heavy object easier?

• The object is moved over a shorter distance.
• The ramp increases the amount of work you do.
• Less force is needed to move the object over a longer distance.
• More force is needed to move the object over a longer distance.

If two people lift identical stacks of books the same distance and one person does the job twice as fast, which of the following has doubled?

• work input
• work output
• power
• efficiency

By comparing the mechanical advantage of two machines that have the same output force, what can you tell about the machine?

• which is bigger
• which has a larger input force
• which has a larger output force
• which makes work easier

Why is the work output of a machine always less than the work input?

• Some work is used to get the machine started
• Some work is used to overcome the friction created by the machine
• Some work is used to keep the machine running
• There isn't enough power present

Which of the following simple machines is NOT a wedge?

• knife
• plow
• chisel
• ramp

Greg applies a force of 100 N to move a box 5 meters. How much work did he do?

• 100 J
• 500 J
• 5 J
• 500 N

If you exert 20 N of force on a screwdriver and it exerts 40 N on a paint can lid, what is the screwdriver's mechanical advantage?

• 2
• 20
• 1
• 40