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A particle of mass m is projected form the ground with an initial speed u₀ at an angle α with the horizontal. At the highest point of its trajectory, it makes a completely inelastic collision with another identical particle, which was thrown vertically upward from the ground with the same initial speed u₀. The angle that the composite system makes with the horizontal immediately after the collision is

1. π/4
2. π/4 + α
3. π/2 - α
4. π/2

Correct answer: π/4

Solution

At the highest point, the horizontal and vertical momentum components of the system combine symmetrically due to the identical particles and their velocities. This results in the composite system moving at an angle of π/4.

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