Energy, Work and Power

A weightlifter lifts two 300 newton weights 1.5 meters off the ground. How much work has she done?

Work = Force x Distance

• 600 J

• 450 J

• 900 J

• 1200 J

Simple machines make work easier by increasing what?

• The distance over which work is done 
• The force needed to do work 
• The time required to do work
• The acceleration of a massive object 

The amount by which a machine multiplies input force is known as the 

• work.
• power.
• output force.
• mechanical advantage.

You do 90 joules of work in 30 seconds. How much power have you generated?

Power = Work/time

• 30 watts
• 3 watts
• 120 watts
• 270 watts

You move a 8 N object five meters in 4 seconds. How much power have you generated?

Work = Force x Distance

Power = Work/Time

• 160 watts

• 10 watts

• 6.4 watts

• 17 watts

Answer explanation

Work(40J) = Force(0.8N) x Distance(5m)

Power(10W) = Work(40J) / Time(4s)

Tags

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When you rub your hands together on a cold day, you use friction to convert

• Mechanical energy into thermal energy

• Thermal energy into nuclear energy

• Chemical energy into mechanical energy.

• Electrical energy into thermal energy

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Which energy-conversion chain occurs whenever coal is burned to create steam to spin the generator at a power station?

• chemical to mechanical to potential

• thermal to chemical to mechanical to electrical

• chemical to thermal to mechanical to electrical

• chemical to chemical to mechanical to radiant

Answer explanation

Water changing to steam does not break any molecular bonds, mechanical energy is harnessed as pressure from the expanded volume of steam

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Light is an example of _________

• thermal energy
• radiant energy
• mechanical energy
• nuclear energy

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Which of the following is defined as work done per unit time?

• A. energy

• B. force

• C. power

• D. work

50 J of work is done lifting a 20.0 N book in the air. How high was it lifted?

Distance = Work/Force

• 2.5 m

• 3.5 m

• 0.4 m

• 25 m

Tags

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