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Lesson: Power

Worksheet: Power • 6 Questions


A motor lifts an elevator that carries a load of mass kg to a height of 23.8 m in a time of 16.2 s. The total mass of the elevator mechanism is kg, including a counterbalancing weight. The elevator and the counterweight both accelerate from rest to a final speed of 3.45 m/s. What is the useful power output of the motor?


A person does 6.00 MJ of useful work in s.

What is the person’s useful power output?

How long will it take this person to lift kg of bricks to a 1.50-m-height platform?


A dragster of mass 465.0 kg accelerates from rest to a final speed of 102.5 m/s over a distance of 415.0 m. The dragster accelerates against an average resistive force of N. What is its average power output if the acceleration takes 6.850 s?


A man of mass 80.0 kg runs up a flight of stairs 20.0 m high in 10.0 s.

How much power is required for the man to rise this far in this time?

If the man’s body has an efficiency of for running up stairs, how much power was required for the run?


A girl pulls her wagon that has a mass of 15 kg along a flat sidewalk with negligible friction by applying a force of magnitude 10 N at an angle of above the horizontal. The wagon is initially at rest.

How much work does the girl do on the wagon during the first 2.0 s that she pulls it along?

How much instantaneous power does she exert at s?


Suppose you have a device that extracts energy from ocean breakers in direct proportion to their intensity. If the device produces 10.0 kW of power on a day when the breakers are 1.20 m high, how much will it produce when they are 0.600 m high?