Practice Power in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The rate at which work is done or energy is transferred, measured in watts (joules per second).

How fast you use or produce energy. A powerful engine does work quickly.

Showing a random 20 of 50 problems.

Example 1

medium

A motor rated

1.2 \text{ kW}

runs for

25 \text{ minutes}

. Total work done?

Example 2

easy

1500 \text{ W}

kettle is on for

30 \text{ s}

. How much energy does it use?

Example 3

easy

A device runs at

40 \text{ W}

for

1 \text{ minute}

. How much energy does it use?

Example 4

medium

A runner (60 kg) climbs stairs 5 m high in 4 s (g = 9.8). Find the power output.

Example 5

easy

A machine delivers 400 J in 2 s and another delivers 400 J in 4 s. Which is more powerful?

Example 6

easy

A force of 50 N moves an object at constant 4 m/s. Find the power delivered.

Example 7

easy

A pump does

1500 \text{ J}

of work in

5 \text{ s}

. What is its power output?

Example 8

challenge

A 75 kg cyclist climbs a hill rising 100 m over a path while maintaining 200 W of useful power (g = 9.8). How long does the climb take?

Example 9

medium

1200 \text{ kg}

car accelerates from rest to

20 \text{ m/s}

10 \text{ s}

. Ignoring friction, find the average power delivered.

Example 10

challenge

A turbine converts the energy of 500 kg of water falling 40 m each second at 80% efficiency (g = 9.8). Find the electrical power output.

Example 11

easy

A 60 W bulb runs 10 s. How much energy does it use?

Example 12

easy

100 \text{ W}

light bulb is on for

2 \text{ hours}

. How much energy does it use?

Example 13

medium

Two cranes each lift a

500 \text{ kg}

load

20 \text{ m}

. Crane A takes

50 \text{ s}

and Crane B takes

100 \text{ s}

. What is each crane's power output? Use

g = 10 \text{ m/s}^2

Example 14

medium

A pump lifts 200 kg of water 15 m in 30 s (g = 9.8). Find the power.

Example 15

medium

60 \text{ kg}

runner climbs

4 \text{ m}

of vertical stairs in

5 \text{ s}

(

g = 9.8

). Find her average power output against gravity.

Example 16

medium

An athlete delivers

1.2 \text{ kJ}

to a barbell in

0.8 \text{ s}

. Find the average power.

Example 17

hard

1000 \text{ kg}

car climbs a

5\%

grade (5 m rise per 100 m) at constant

20 \text{ m/s}

(

g = 9.8

). Find the engine power against gravity alone.

Example 18

medium

200 \text{ W}

pump runs

15 \text{ minutes}

. Express the energy used in kilojoules.

Example 19

medium

A crane lifts a 500 kg beam 12 m in 8 s at constant speed (g = 9.8). Find the power.

Example 20

medium

2.5 \text{ kW}

heater runs for

30 \text{ minutes}

. How much energy (in joules) does it use?

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Related Concepts

Work Energy Electrical Power