A projectile is fired with speed u at angle θ. When its horizontal coordinate is R/4, its velocity is:
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A projectile is fired with speed u at angle θ. When its horizontal coordinate is R/4, its velocity is:

G1 Physics · Accepted Answer

Horizontal speed remains u cosθ. Since x is proportional to time, x/R = t/T. At x=R/4, t=T/4. Now T = 2u sinθ/g. Therefore vᵧ = u sinθ − g(T/4) = u sinθ − u sinθ/2 = u sinθ/2. Hence velocity vector = u cosθ î + (u sinθ/2) ĵ.