Q21 of 101 Page 132

A projectile is fired from the top of a 40 m high chit with an initial speed of 50 m/s at an unknown angle. Find its speed when it hits the ground.

Height from where the projectile is fired, h = 40 m

Initial speed of the projectile, u = 50 m/s


Final speed at which the projectile hits the ground = v m/s


Acceleration due to gravity, g = 10 m/s2


Using the equation of motion, v2 - u2 = 2gh


⇒ v2 = u2 + 2gh


⇒ v2 = 502 + 2×10×40


⇒ v2 = 2500 + 800


⇒ v2 = 3300


⇒ v = 57.45 m/s


∴ The projectile hits the ground with a speed of 57.45 m/s


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