A ball is launched horizontally from the top of a 20 m tall building. It hits the ground making a 45 deg angle with the horizontal. What was the initial speed of projection (in m/s)?

Correct answer: 20

Solution

For a 45 deg impact angle, the horizontal speed equals the vertical speed just before hitting the ground. Using kinematics, vy = sqrt(2 * 10 * 20) = 20 m/s, so the projection speed vx = 20 m/s.

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