A stone is dropped from the top of a tower of height `h`. Aftre `1 s` another stone is droppped from the balcony `20 m` below the top. Both reach the bottom simultaneously. What is the value of `h` ? Take `g=10 ms^(-2)`.

Options

A. 43125m
B. 312.5m
C. 31.25m
D. 25.31m

Answer

C

Explanation

`h=(1)/(2)"gt"^(2)` and `h-20=(1)/(2)g(t-1)^(2)`
`(1)/(2)"gt"^(2)-20=(1)/(2)"gt"^(2)-20=(1)/(2)"gt"^(2)-gt+(g)/(2)`
`gt=20+(g)/(2)`
`10t=20+5rArr t=2.5`
`h=(1)/(2)"gt"^(2)=(1)/(2)xx10xx(2.5)^(2)`
`=5xx6.25=31.25m`