Question

The velocity of a body of mass 10 kg increases from 4 m/s to 8 m/s when a force acts on it for 2 s.
(a) What is the momentum before the force acts ?
(b) What is the momentum after the force acts ?
(c) What is the gain in momentum per second ?
(d) What is the value of the force ?

Answer 1

(a) Momentum = Mass × velocity
= 10 × 4
= 40 kg.m/s

(b) Momentum = Mass × velocity
= 10 × 8
= 80 kg.m/s

(c) The gain in momentum per second = Momentum Gaintime
= ${\displaystyle \frac{80-40}{2}}$
= ${\displaystyle \frac{40}{2}}$
= 20  ${\displaystyle {\text{kg.m/s}}^2}$
(d) Force is the rate of change of momentum or the momentum gain or lost per second.
So, force = 20 kg.ms/² = 20 N