Power Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Power.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept 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.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Power measures how quickly energy is transferred — the same work done faster requires more power.

Common stuck point: A small motor can do the same work as a big motor—it just takes longer.

Sense of Study hint: When solving a power problem, first determine whether you know work and time or force and velocity. Then use P = W/t if you have work done over a time interval, or P = Fv if you have a constant force and velocity. Finally, check that your units are in watts (joules per second).

Worked Examples

Example 1

easy
A motor does 6000 \text{ J} of work in 30 \text{ s}. What is the power output?

Solution

  1. 1
    Use the power formula: P = \frac{W}{t}.
  2. 2
    Substitute the values: P = \frac{6000}{30}.
  3. 3
    P = 200 \text{ W}

Answer

P = 200 \text{ W}
Power is the rate of doing work or transferring energy. It tells us how quickly energy is used, not just how much.

Example 2

medium
A 70 \text{ kg} person runs up a 5 \text{ m} staircase in 4 \text{ s}. What is the power output? Use g = 9.8 \text{ m/s}^2.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
A 100 \text{ W} light bulb is on for 2 \text{ hours}. How much energy does it use?

Example 2

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.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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