A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration and change in momentum. Also calculate the magnitude of the force required.

Given,

Initial velocity, u = 90 km/h


=


= 25 m/s


Final velocity, v = 18 km/h


=


= 5 m/s


Acceleration, a =?


Time, t = 4 s


Now, v = u + at


5 = 25 + a × 4


4a = 5 – 25


4a = - 20


a = -


a = - 5 m/s2


Therefore, the acceleration of the motorcar is -5 m/s2.


Now we will calculate change in momentum:


Change in momentum = mv – mu


= 1200 × 5 - 1200 × 25


= 6000 – 30000


= - 24000 kg m/s


Therefore, change in momentum is 24000 kg m/s


Now we will calculate the magnitude of force:


Force, F = m × a


= 1200 × (-5)


= - 6000 N


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