Question

A ball projected with a velocity of `10m//s` at angle of `30^(@)` with horizontal just clears two vertical poles each of height `1m`. Find separation between the poles.

Answer 1

`h=u_(y)t+1/2g t^(2)=(10sin 30^(@))t+1/2(-10)t^(2)`
`1=5t-5t^(2) rArr t=0.72s,2.76s` are the instants at which projectile crosses the poles
`:.` Separation between poles `=OS-OQ`
`=u cos theta (t_(2)-t_(1))`
`=10cos 30^(@)(2.72-0.72)=17.7m`