Two planes of the same mass collide head-on and becomes tangled so that they move on together. If the engines of both were stopped at the moment of impact and the speeds of the planes at impact were 120m/s and 200 m/s, find the joint velocity immediately after collision.

Answer 1

Apply the conservation of momentum law, using the appropriate sign for velocity. If the 120 m/s plane (#1) is going in the + direction, the 200 m/s plane (#2) is going in the - direction.

Each plane has mass M.
Momentum conservation requires:

MV1 -MV2 = 2M*Vfinal

Vfinal = (1/2)(V1 - V2) = -40 m/s

Answer 2

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