A car of mass 1ton is moving with a velocity of 25 m/s towards left. A truck of mass 5 ton is moving towards left with a velocity of 3 m/s. If the collision is perfectly elastic, what is the final velocity of the truck in m/s?

(a) 11

(b) 25

(c) 3

(d) 10

This question was posed to me in my homework.

This question is from Collision topic in section Work, Energy and Power of Physics – Class 11

Select the correct answer from above options

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Right choice is (c) 3

To explain: The initial momentum of the system = momentum of car + momentum of truck = 40 Kg-m/s leftwards. Since the momentum is conserved, the initial momentum = final momentum. Hence the final momentum is 40 Kg-m/s leftwards. The collision is perfectly elastic, therefore, e = 1. Therefore, final relative velocity (of truck with respect to car) = initial relative velocity (of truck with respect to car). Sum of the final velocities of the car and the truck = 4 m/s. From this information and the conservation of momentum, one can find the final velocity of the truck.