Worksheet: Work, Energy, and Mechanical Advantage

Using a lubricant, like graphite, increases the efficiency of machines because it reduces friction.

• It reduces friction

• It increases friction

• It blocks energy transfer

• It decreases machine temperature

Two students are moving 95-N cartons of books from the floor to a platform. One student moves 10 cartons in 5 minutes and the other student moves 10 cartons in 7 minutes. Which student does more work on her cartons?

• The first student does more work

• The second student does more work

• Both students do the same amount of work

• It cannot be determined from the given information

In simple machines, what happens to the output force when the effort force is increased? Fill in the blank: "If a machine is used to produce a greater effort force, ____________ is decreased." Explain your answer.

• the output force

• the efficiency

• the speed of the machine

• the mechanical advantage

Choose the correct statement regarding wrench usage: When a wrench is used to tighten a bolt, the diameter of the handle is more important than the length; when a wrench is used to loosen a bolt, the length is more important than the diameter.

• Both statements are correct.

• Only the statement about tightening is correct.

• Only the statement about loosening is correct.

• Neither statement is correct.

Emily carries several bricks across a yard and hands them to a builder. Her friend tells her that she is doing no work on the bricks because the force she uses (vertical to counter gravity) is perpendicular to the horizontal displacement of the bricks. How could Emily accomplish the same tasks while doing work on the bricks?

• By moving the bricks downward.

• By lifting the bricks upward (against gravity) over a vertical displacement.

• By moving the bricks horizontally.

• By not changing the position of the bricks.

Work increases the kinetic energy of an object by applying a force that causes the object to accelerate. Which example correctly illustrates this effect?

• A person pushing a car causing it to accelerate

• Friction slowing down a sliding object

• Air resistance decreasing the speed of a falling object

• A stationary book remaining at rest on a shelf

When the force is applied perpendicular to the direction of motion, work done is calculated using the formula W = F × d × cosθ. Since for a perpendicular force, θ = 90° and cos 90° equals 0, no work is done on the object.

• Because cos 90° equals 0, making the work done equal to 0.

• Because the object does not move.

• Because the distance d is 0.

• Because energy is transformed to heat.

A 6.50 N weight is raised from the ground to 2.00 m above the ground. How much work is done on the weight?

• 13.00 J

• 6.50 J

• 2.00 J

• 10.00 J

A worker uses an ideal machine to lift a 12.0-N weight a distance of 5.00 m. If the worker applies a force of 6.00 N, how far does the effort force move?

• 10.0 m

• 5.00 m

• 15.0 m

• 20.0 m

An effort force of 300.0 N is applied to an ideal machine. The effort force moves a 750.0-N object a distance of 250.0 cm. What is the mechanical advantage of the machine?

• 2.5

• 1.5

• 3.0

• 2.0