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 kW1.2 \text{ kW} runs for 25 minutes25 \text{ minutes}. Total work done?

Example 2

easy
A 1500 W1500 \text{ W} kettle is on for 30 s30 \text{ s}. How much energy does it use?

Example 3

easy
A device runs at 40 W40 \text{ W} for 1 minute1 \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 J1500 \text{ J} of work in 5 s5 \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
A 1200 kg1200 \text{ kg} car accelerates from rest to 20 m/s20 \text{ m/s} in 10 s10 \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
A 100 W100 \text{ W} light bulb is on for 2 hours2 \text{ hours}. How much energy does it use?

Example 13

medium
Two cranes each lift a 500 kg500 \text{ kg} load 20 m20 \text{ m}. Crane A takes 50 s50 \text{ s} and Crane B takes 100 s100 \text{ s}. What is each crane's power output? Use g=10 m/s2g = 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
A 60 kg60 \text{ kg} runner climbs 4 m4 \text{ m} of vertical stairs in 5 s5 \text{ s} (g=9.8g = 9.8). Find her average power output against gravity.

Example 16

medium
An athlete delivers 1.2 kJ1.2 \text{ kJ} to a barbell in 0.8 s0.8 \text{ s}. Find the average power.

Example 17

hard
A 1000 kg1000 \text{ kg} car climbs a 5%5\% grade (5 m rise per 100 m) at constant 20 m/s20 \text{ m/s} (g=9.8g = 9.8). Find the engine power against gravity alone.

Example 18

medium
A 200 W200 \text{ W} pump runs 15 minutes15 \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
A 2.5 kW2.5 \text{ kW} heater runs for 30 minutes30 \text{ minutes}. How much energy (in joules) does it use?
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