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A body is projected vertically upwards w...

A body is projected vertically upwards with some velocity `u`. It is at the same point at `t = 6 s` as was at `t = 4 s`. Find the value of `u`.

A

`30 m//s`

B

`40 m//s`

C

`20 m//s`

D

`50 m//s`

Text Solution

Verified by Experts

The correct Answer is:
D
At `t_1 = 4s` and `t_2 = 6 s`, body is at height `h`
So `h = ut_1 - ((1)/(2)) g t_1^2`
and `h = ut_2 - ((1)/(2)) g t_2^2`
Solve to get `u = (1)/(2) g(t_1 + t_2)`
=`(1)/(2) xx 10(4 + 6) = 50 m//s`
Time of flight : `T = t_1 + t_2`
`(2 u)/(g) = T rArr (2 u)/(10) = 10 rArr u = 50 m//s`.
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