Trajectory of particle in a projectile motion is given as y = x - x²/80. Here, x and y are in metres and considered along horizontal and vertical direction respectively (g = 10 m/s²). For this projectile motion.
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Question

Trajectory of particle in a projectile motion is given as y = x - x²/80. Here, x and y are in metres and considered along horizontal and vertical direction respectively (g = 10 m/s²). For this projectile motion.

Options

G1 Physics · Accepted Answer

Compare y = x - x²/80 with y = x tanθ - gx²/(2uₓ²). Thus tanθ = 1, so θ = 45°. Also 1/80 = 10/(2uₓ²), giving uₓ = 20 m/s and uᵧ = 20 m/s. Hence H = 20 m and R = 80 m; after 4 s vᵧ = -20 m/s, so the velocity angle is 45° downward. Only option A is correct.