Linear Momentum (CIE A Level Physics)

A tennis ball of mass, m = 60 g travels at a velocity, v = 75 m s^-1. A brick of mass, m = 3 kg travels at a velocity, v = 1.5 m s^-1.

Determine which object has the most momentum.

Answer: 

Step 1: List the known quantities and convert to SI units

• Mass of tennis ball, 
• Velocity of tennis ball, $v_T = 75 \mathrm{m} {\mathrm{s}}^{-1}$
• Mass of brick, $m_B = 3 \mathrm{kg}$
• Velocity of brick, $v_B = 1.5 \mathrm{m} {\mathrm{s}}^{-1}$

Step 2: Determine the momentum of the tennis ball

$p_T = m_T \times v_T$

$p_T = 0.06 \times 75$

$p_T = 4.5 \mathrm{kg} \mathrm{m} {\mathrm{s}}^{-1}$

Step 3: Determine the momentum of the brick

$p_B = m_B \times v_B$

$p_B = 3 \times 1.5$

$p_B = 4.5 \mathrm{kg} \mathrm{m} {\mathrm{s}}^{-1}$

Step 4: State which object has the most momentum

• Both objects have the same momentum
  • Even though the brick has a greater mass, it has a much lower velocity than the tennis ball