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A ball is droped from a high rise platfo...

A ball is droped from a high rise platform `t = 0` starting from rest. After `6 s` another ball is thrown downwards from the same platform with a speed `v`. The two balls meet at `t = 18 s`. What is the value of `v` ?

A

1) `75ms^(-1)`

B

2) `55ms^(-1)`

C

3) `40ms^(-1)`

D

4) `60ms^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
A
For first ball ,u = 0
`S_(1)=(1)/(2)gt_(1)^(2)=(1)/(2)g(18)^(2)`
For second ball , initial velocity =v
`therefores_(2)=vt_(2)+(1)/(2)gt_(2)^(2)`
`t_(2)=18-6=12s`
`Rightarrows_(2)=S_(2)=vxx12+(1)/(2)g(12)^(2)`
Her `s_(1)=(s_(2)`
`(1)/(2)g(18^(2))=12v+(1)/(2)g(12)^(2)Rightarrowv=74ms^(-1)`
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