A variable mass body with an initial mass of 18 kg is moving with a velocity of 3 m/s initially, after some time the velocity increases to 12 m/s, what is the new mass if the body is moving in the absence of any external force?
Answer & explanation
Correct answer: option 2
If no net external force acts on the system, the total momentum is conserved.
$m_1 v_1 = m_2 v_2$
$18 \text{ kg x } 3 \text{ m/s} = m \text{ x } 12 \text{ m/s}$
$\Rightarrow m = \frac{54}{12} \text{ kg }$
$\Rightarrow m = 4.5 \text{ kg}$