Work, Force, and Power Review

George uses 15 N of force to move a box of books 20 m.

How much work did he do?

W= F x d 

• 1.33 J

• 0.75 J

• 300 J

• 300 N

A crane lifts an 8,000 N beam, 80 m to the top of a building in 50 s. Using the equation P= W/t, calculate how much power the crane uses.

W= F x d

P = W/t

• 13,800 W

• 9,800 W

• 12,800 W

• 10,800 W

Tags

NGSS.MS-PS3-4

An example of work not being done is:

• A man carrying a tray across the room.

• A woman lifting a baby out of bed.

• A child pushing his baby brother in a stroller.

• A man pulling his boat out of the water from a boat launch.

In order for work to happen a force must be applied and:

• The object must move in the same direction as the applied force.

• The object is not moving or moving in a straight line at a constant speed.

• The direction has no bearing on the force.

• The object must move in the opposite direction as the force.

Which of the following actions do more work on an object?  

• Lifting an 90 N box 1 m up off the floor

• Lifting a 90 N box 3 m up off the floor

• Lifting a 100 N box 1 m up off the floor

• Lifting a 100 N box 3 m up off the floor

Tags

NGSS.MS-PS3-5

A force of 30 N is applied to a crowbar to pry the lid off of a can of paint. The crowbar applies 75 N of force to the lid. What is the mechanical advantage of the crowbar?

Mechanical Advantage = Output Force/Input Force

• 0.4

• 2.5

• 45

• 30

Which takes more power: using 15 N to lift a ball 2 meters in 5 seconds or using 100 N to push a box 2 meters in 60 seconds?

P = W/t

W = F x d

• 15 N to lift a ball 2 meters in 5 seconds

• 100 N to push a box 2 meters in 60 seconds

Tags

NGSS.HS-PS3-2

If a simple machine has a mechanical efficiency of 95%, what might be the reason that a machine can never be 100% efficient?

• The machine is broken

• Friction of moving parts.

• The machine does not have mechanical advantage.

• The operator of the machine does not know how to use it.

Tags

NGSS.MS-ETS1-1

An engine does 45,000 J of work in 30s. What is the power of the motor?

P = W/t

• 1,350,000 W

• 1500 W

• 0.00067 W

• 200 W

A ramp is used to load furniture onto a moving truck. The person does 1240 J of work pushing the furniture up the ramp, and the ramp does 822 J of work. Calculate the mechanical efficiency of the ramp.

Mechanical Efficiency = (Work Output/Work Input) x 100%

• 151%

• 100%

• 66.3%

• 50%