calculate the change in momentum of a car of mass 1000 kg when its speed increases from 36 km/h to 108 km/h uniformly?

Answer :

m = 1000 kg
v1 = 36 km/h = 10 m/s
v2 = 108 km/h = 30 m/s
p1 = 1000×10
    = 10000 kg m/s
p2 = 1000×30
    = 30000 kg m/s
Change = (30000-10000) kg m/s
20000 kg m/s
The change will be occur in Car direction where it was going before change.
Change in momentum does not depend on whether the speed changes uniformly or not.  We have to assume that the car is traveling in one direction only.  Since speed is specified and not velocity.  Momentum is a vector. SO we find its magnitude and direction.

V1 = 36kmph = 36*5/18 = 10 m/sec
V2 = 108 kmph = 30 m/sec

Change in momentum = final momentum - initial momentum
               = p2 - p1    = m V2 - m V1  =  m (V2 - V1)

Magnitude of change in momentum   = 1000 (30 -10)  = 20,000 kg-m/sec

Change in momentum is +ve and it means that its direction is in the direction of motion of the car.

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