Momentum (Oxford AQA IGCSE Physics)

Worked Example

Determine which object has the greatest momentum, the tennis ball or the brick.

Explain your answer.

Answer:

Step 1: Calculate the momentum of the tennis ball

p = m × v

p = 0.06 × 75

p = 4.5 kg m/s 

Step 2: Calculate the momentum of the brick

p = m × v

p = 3 × 1.5

p = 4.5 kg m/s

Step 3: Explain your answer

• Both the tennis ball and the brick have the same momentum

• Even though the brick has a much greater mass than the ball, the ball is travelling much faster than the brick

• This means that on impact, they would both exert a similar force (depending on the time it takes for each to come to rest)

Exam Tip

The unit of velocity, m/s, is sometimes written as m s^-1, therefore the unit of momentum is sometimes written as kg m s^-1. You are not expected to know this for your exam but you may see some resources use this notation.

Which direction is taken as positive is completely up to you in the exam. In general, forwards, to the right, and upwards are taken as positive, and backwards, to the left, or down are taken as negative.