Work, Energy and Power

_______ is defined as the rate at which work is done.

• Efficiency

• Power

• Work

• Kinetic Energy

A boy pushes on a parked car with a force of 250N. The car does not move. How much work does the boy do?

• 250J

• 250N

• 0J

• 2500J

A man pushes a crate along a factory floor by exerting a force of 55N. If the crate moves a distance of 4m, how much work does the man perform?

• 550J

• 2200J

• 220N

• 220J

A weightlifter presses a 400N weight 0.6m over his head in 2s. What is the power of the weightlifter?

• 120W

• 1200W

• 200W

• 240W

In which of the situations is NO work being done?

• pushing a box across the floor

• lifting a box from the ground to a table top

• holding a box overhead

• carrying a box up a flight of stairs

As a dropped coin falls toward the ground, ____ energy is converted to ____ energy.

• heat, kinetic

• potential, heat

• kinetic, potential

• potential, kinetic

The law of conservation of energy states that energy

• can only be converted into heat

• cannot be created or destroyed

• is created from motion.

• is always opposite.

A worker carrying a box of mass 20 kg to a height of 2.5m. Calculate the work done by the worker in carrying the box.

• 49.05J

• 490.5J

• 4950J

• 1000J

A boy of mass 51kg climbed up a staircase of height 4m in 5s. Calculate the power delivered by the boy

• 255W

• 204W

• 2001.24W

• 400.25W

A motor rated 100W has been operating for 150s. If the efficiency of the motor is 75%, how much work is done by the motor?

• 1125000J

• 1125J

• 11250J

• 24000J