An elevator of mass M is accelerated upwards by applying a force F.A mass m initially situated at a height of 1 m above the floor the elevator is falling freely. It will hit the floor of the elevator after a time equal to

Options

A. `sqrt((2M)/(F+mg))`
B. `sqrt((2M)/(F-mg))`
C. `sqrt((2M)/(F))`
D. `sqrt((2M)/(F+Mg))`

Answer

C

Explanation

`a_(e)=(F)/(m)uarr`
`a_(s)=-gdarr`
`a_(s//e)=a_(s)-a_(e)=(F)/(m)+g=(F+Mg)/(M)`
`s=ut+(I)/(2)at^(2)`
`1=(1)/(2)((F+Mg)/(M))t^(2)`
`t=sqrt(2(M)/(F+Mg))`