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.

Question

Physics

Mariana Haney

10 February, 20:16

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.

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Justine Fry · 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