The trajectory of a projectile is y=3x−x²/20, where x and y are in metre. Taking g=10 m s⁻², which set gives its horizontal range R, maximum height H and projection speed u?

Question

G1 Physics · Accepted Answer

The trajectory has the form y=ax−bx², with a=3, b=1/20. Range: R=a/b = 3/(1/20) = 60 m. Maximum height: H=a²/(4b) = 9/[4(1/20)] = 45 m. Projection speed: u² = g(1+a²)/(2b) = 10(1+9)/(2/20) = 1000. Therefore u=10√10 m s⁻¹. Hence option B is correct.