An automobile engine propels a 1000 kg car (A) along a levelled road at a speed of 36 km h–1. Find the power if the opposing frictional force is 100 N. Now, suppose after travelling a distance of 200 m, this car collides with another stationary car (B) of same mass and comes to rest. Let its engine also stop at the same time. Now car (B) starts moving on the same level road without getting its engine started. Find the speed of the car (B) just after the collision.
Mass of the car = 1000 Kg
Speed, V = 36 km/hr = (36 x 1000)/3600 = 10 m/s
Frictional force, k = 100 N
Power = k. V = 100 x 10 = 1000W
After collision of both the cars, according to law of conservation of momentum,
mAuA + mBuB = mAvA + mBvB
⇒ 1000 x 10 + 1000 x 0 = 1000 x 0 + 1000 x vB
⇒ vB = 10m/s
Therefore, the speed of the car (B) just after the collision is 10m/s.