A ball is thrown horizontally from the top of a 20m high hill. It strikes the ground at an angle of 45°. With what speed was it thrown?
Answer: 20 m/s
Explanation
Ball falls 20m, so time taken is found using:
s = 1/2 gt²
20 = 1/2 × 10 × t²
t = 2s
Vertical velocity when it hits the ground:
v_y = gt = 10 × 2 = 20 m/s
Since it hits at 45°, v_x = v_y = 20 m/s
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