WORK, POWER, AND ENERGY REVIEW

Which of the following best defines *work* in physics?

• A person completing a task

• Energy transferred when a force moves an object through a distance

• Energy stored in food

• The rate of doing something

A force of 40 N pushes a box 2 m forward. How much work is done?

• 20 J

• 42 J

• 80 J

• 0 J

Which of the following is **not** an example of work in the physics sense?

• Carrying a bag while standing still

• Lifting a dumbbell above your head

• Pulling a sled across snow

• Pushing a door open

What is the SI unit of work?

• Watt

• Joule

• Newton

• Pascal

Which equation correctly represents work?

• W = F × d × cosθ

• W = F/d

• W = m × g

• W = P × t

A student lifts a 5 kg backpack 2 m high. Take g = 9.81 m/s². How much work is done?

• 1.01 J

• 24.53 J

• 54.32 J

• 98.1 J

Power is defined as:

• Work × Force

• Work ÷ Time

• Energy ÷ Distance

• Force × Acceleration

A machine transfers 400 J of energy in 20 s. What is its power?

• 10 W

• 20 W

• 40 W

• 80 W

The efficiency of a machine is always less than 100% because:

• Some energy is lost as heat due to friction

• Work input is always less than work output

• Energy disappears

• Machines create extra energy

A motor uses 1200 J of energy and produces 900 J of useful work. What is its efficiency?

• 25%

• 50%

• 75%

• 100%