Question
By how much does the momentum of a body of mass 5 kg change when its speed
(i) decreases from 20 m/s to 0.20 m/s; and
(ii) increases from 30 m/s to 40 m/s?
Solution
(i) Here,
Mass of the body, m = 5 kg
Initial velocity, u = 20 m/s
Final velocity, v = 0.20 m/s
Change in momentum = m(v - u)
= 5(0.20 - 20) kg m/s
= -99 kg m/s
The negative sign shows that the momentum decreases.
(ii) Here,
Mass, m = 5 kg
Initial velocity, u = 30 m/s
Final velocity, v = 40 m/s
Change in momentum = m(v - u)
=5(40-30)
= 50 kg m/s
Here, the momentum of the body decreases, when it's speed increases.
