A projectile is thrown with velocity v making an angle θ with the horizontal. It just crosses the top of two poles, each of height h, after 1 second and 3 second respectively. The time of flight of the projectile is
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Question

A projectile is thrown with velocity v making an angle θ with the horizontal. It just crosses the top of two poles, each of height h, after 1 second and 3 second respectively. The time of flight of the projectile is

Options

G1 Physics · Accepted Answer

For vertical motion, y = uᵧt - ½gt². The projectile is at the same height h at t₁ = 1 s and t₂ = 3 s. These are the two roots of ½gt² - uᵧt + h = 0, whose sum is t₁ + t₂ = 2uᵧ/g, equal to the total time of flight. Thus T = 1 + 3 = 4 s. Hence option C.