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An automobile engine propels a 1000 kg car (A) along a levelled road at a spedd of 36 km//h. Find the power if the opposing frictional force is 100 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.

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Mass of the car `A, m_A = 1000kg`
Mass of the car `B, m_B = 1000kg`
initial velocity of car `A, u_A= 36 km//h = 36 ((5)/(18))m//s = 10m//s (as 1km//h = (5)/(18)m//s)`
Opposing force of friction, `F = 100 N`
Power of the engine of car `A = F u_A = (100N) (10m//s) = 1000 W`
`("as power" ="force" x "velocity"` and `N m//s = J//s =W)`
Initial velocity of car `B, u_B = 0`
Final velocity of car `A, upsilon_A = 0 ("as it comes to rest after colliding with car B")`
If `upsilon_B` is final velocity of car B when car A collides with it applying the law conservation of momentum,
initial momentum of cars A and B = final momentum of cars A and B
`i.e., m_A u_A + u_B u_B = m_A upsilon__B`
or `1000 xx 10 + 1000 xx 0 = 1000 xx 0 + 1000 xx upsilon_B`
or `upsilon_B = 10m//s`

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