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

Explanation

`h=40m, u=50m/sec`
let the speed be v when it strikes the ground.
Applying law of conservation of energy,
`mgh+1/2mu^2=1/2mv^2`
`rarr 10xx40+(1/2)xx2500=1/2v^2`
`rarr v^2=3300`
`rarr v=57.4m/sec=58m/sec`