A car of mass 1000 kg rests on a horizontal road initially . It is then pushed over 5 m to a speed of 1 m/s before the engine is started . If the average frictional force acting on the car is 500 N,the total work done in moving the car before the driver starts the engine is.

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2015-11-08T13:08:07+05:30

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Case 1:  The car is pushed from rest to a speed of 1m/s  over a distance of 5 m.
     So the car is accelerated during this push.

KE of the car gained due to pushing = 1/2 m v² = 1/2 * 1000 kg * 1² (m/s)²
       = 500 J
Work done against friction = friction force * displacement
       = 500 N * 5 m = 2,500 J

Total work done in moving the car from rest to a speed of 1 m/s
    = 2,500 + 500 = 3, 000 J

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Case 2.  The car is pushed at a uniform speed of 1 m/s  over 5 m

Work done in moving the car is against the friction force.
   W = F s = 500 N * 5 m = 2,500 J

Since the car is pushed at a uniform speed, the force exerted is equal to the friction force.

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