A projectile is projected with velocity of 25 m/s at an angle θ with the horizontal. After t seconds its inclination with horizontal becomes zero. If R represents horizontal range of the projectile, the value of θ will be [use g = 10 m/s²]
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Question

A projectile is projected with velocity of 25 m/s at an angle θ with the horizontal. After t seconds its inclination with horizontal becomes zero. If R represents horizontal range of the projectile, the value of θ will be [use g = 10 m/s²]

Options

G1 Physics · Accepted Answer

The inclination becomes zero at the highest point, so u sinθ = gt. Also R = u²sin2θ/g. Substituting u = gt/sinθ gives R = 2gt²cotθ. Therefore cotθ = R/(2gt²) = R/(20t²), so θ = cot⁻¹[R/(20t²)]. Hence option D.