Question

A loaded lorry of mass 12000 kg moves with a velocity of 12 m/s. Its
velocity becomes 10 m/s after 5 s.
a) What is the initial momentum and what is the final momentum ?
b) What is the change in momentum?
c) What is the rate of change of momentum?​

Answer 1

Given :

• Mass = 12,000 kg
• Initial velocity = 12 m/s
• Final velocity = 10 m/s
• Time = 5 s

Solution :

(a)

Initial momentum (Pi)

⇒ Pi = m x u

⇒ Pi = 12000 x 12

⇒ Pi = 144000 kg m/s

Final Momentum (Pf)

⇒ Pf = m x v

⇒ Pf = 12000 x 10

⇒ Pf = 120000 kg m/s

(b) Change in momentum ( ΔP )

⇒ ΔP = Pf - Pi

⇒ ΔP = 120000 - 144000

⇒ ΔP = - 24000

The rate of change of momentum is - 24000 kg m/s .

(c) Rate of change in momentum (F)

⇒ F = ΔP / t

⇒ F = - 24000 / 5

⇒ F = - 4800 N

⇒ | F| = 4800 N

The magnitude of rate of change of momentum (force ) is 4800 N .