Calculating Power (GCSE Physics)

Calculating Power

The Power Equation

Different Formulae for Calculating Power

We can calculate a value for power using two different formulas. The first involves energy and the second involves work done.

1) Energy Transferred

Where:

• Power, P in watts, W
• Energy transferred, E, in Joules, J
• Time, t, in seconds, s

Question: Marianne switches on a toaster for 50 seconds. During this time, the toaster uses 700J of electricity. Calculate the power of the toaster.

1. Write out the appropriate equation.
   For this question, the correct equation is:

2) Work Done

Where:

• power, P, in watts, W
• time, t, in seconds, s
• work done, W, in joules, J

Question: What is the power of a car engine that does 4500J of work in 1.5 minutes?

1. Write out the appropriate equation.
   In this situation, the appropriate equation is:

Question: An athlete of mass 60kg jumps 1.8 metres vertically. The work done in jumping this height was completed in 0.5s.

Calculate the work done and power developed by the athlete.

Question: Work, energy and power are closely linked. Below are four statements.

1. Work done is equal to the useful energy output of a process.
2. The higher the power of a system, the more efficient it is.
3. A force of 10000N applied through a distance of 5 metres will lead to 50kJ of work being done.
4. 1kW means that 1kJ of energy is produced every 1000 seconds.

Which of the statements is / are true?