Question

A motor car of mass 1200kg is moving along a straight line with uniform velocity of 90km/hr. Its velocity is slowed down to 18km/hr in 4s by an unbalanced external force. Calculate the acceleration and change in momentum. Also calculate the external force acting on it.

Answer 1

initial velocity (u) = 90km/hr = 90/3.6 m/s = 25m/s
final velocity (v) = 18km/hr = 18/3.6 m/s = 5m/s
acceleration = (v-u)/t = (5-25)/4 = -5 m/s2
change in momentum = m(v-u) = 1200(5-25) = -24000 kg•m/s
F = ma = 1200 x -5 = -6000 N