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A ball is thrown vertically upwards from...

A ball is thrown vertically upwards from the ground It crosses a point at the height of `25 m` twice at an interval of `4 secs`. The ball was thrown with the velocity of.

A

`20m//s`

B

`25m//s`

C

`40m//s`

D

`30m//s`

Text Solution

Verified by Experts

The correct Answer is:
D
A ball is ………..
`S = 25m`, u = ?
`t_(Q) = t_(1) =4s`
`a = 10m//s^(2)`
`S = ut + (1)/(2)at^(2)`
`25 = ut + (1)/(2) (-10)t^(2)`
`5t^(2) - ut+25=0`
`t_(1) +t_(2) = (u)/(5)`
`t_(1)t_(2) =5`
now `t_(Q) - t_(1) = sqrt((t_(1)+t_(2))^(2) -4t_(1)t_(2))`
`4 = sqrt(((u)/(5))^(2) - 4xx5)`
`u = 30m//s`
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