A ball projected with speed u at angle of projection 15° has range R. The other angle of projection at which the range with same initial speed u is R is:
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Question

A ball projected with speed u at angle of projection 15° has range R. The other angle of projection at which the range with same initial speed u is R is:

G1 Physics · Accepted Answer

For the same speed on level ground, R = u²sin2θ/g. Equal ranges require sin2θ₁ = sin2θ₂, so the two launch angles are complementary: θ₁ + θ₂ = 90°. Thus θ₂ = 90° - 15° = 75°, option C.