A projectile is projected with speed 20 m/s from a point on an inclined plane making an angle 30° above the horizontal. It is projected at the angle that gives maximum range along the inclined plane. Neglect air resistance and take g = 10 m/s². The time of flight before it strikes the inclined plane again is:
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Question

A projectile is projected with speed 20 m/s from a point on an inclined plane making an angle 30° above the horizontal. It is projected at the angle that gives maximum range along the inclined plane. Neglect air resistance and take g = 10 m/s². The time of flight before it strikes the inclined plane again is:

Options

G1 Physics · Accepted Answer

For maximum range along the incline, θ = 45° + α/2 = 45° + 15° = 60°. The time to strike the inclined plane is T = [2u sin(θ - α)]/[g cosα]. Thus T = [2(20)sin30°]/[10cos30°] = 20/(5√3) = 4/√3 s. Therefore option B is correct.