Rain falls vertically downward with constant speed 20 m/s. A man starts from rest and accelerates horizontally with constant acceleration 5 m/s². At what time will the rain appear to him at 45° with the vertical?
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Question

Rain falls vertically downward with constant speed 20 m/s. A man starts from rest and accelerates horizontally with constant acceleration 5 m/s². At what time will the rain appear to him at 45° with the vertical?

Options

G1 Physics · Accepted Answer

At time t, the man's speed is v M v_M v M ​ = at = 5t. The apparent angle θ from the vertical satisfies tanθ = v M / 20 v_M/20 v M ​ /20 = 5t/20. For θ = 45°, tan45° = 1, so 5t = 20 and t = 4 s. Hence option B is correct.