Question

3. Three point masses, "m", "3m" and "4m" lie in a line in deep space away from any gravity. The m and 4m masses are originally at rest and the 3m mass is moving with a speed v in the direction of 4m. All collisions are head-on and elastic. Given [m, v] Determine a. the recoil speed of the 3m mass after hitting the 4m mass. b. the speed of the 3m mass after hitting the m mass. c. the total momentum of the 3 masses after all collisions have occurred. ( ) ( ) M 3m у

Answer 1

For an elastic collision momentum and kinetic energy are conserved.

i. e momentum before collision is equal to momentum after collision. Here before collision only the body with mass 3m is moving with velocity v. Hence the momentum before collision is 3mv.

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