yes de ans is 4 (root)2h/g

 

let me explain in detail...

 

luk here height is - h

so velocity at th surface of water must be (root)2gh................1

 

now wen de object reachez de surface it goes down due to inertia....

 

force acting on body:

 

a: Mg downwards

b: mg upward (m is de mass f water displaced )

so

 

Mg - mg = Ma

 

here M = Vd

m = VD = 2Vd

 

thus, Vdg - 2vdg = Ma or

 

-Vdg = Ma

 

-Mg = Ma

 

hence a= -g.(ie upward)........................2

 

v^2 - u^2 = 2as

here v=0

hence

 

2gh = 2gs

 

s=h

 

ie it will go down a dist of h.....time take for this is root2h/g

 

therefore total time taken while going down is 2 root 2h/g.......3

 

then the object will go up coz of the acc g in upward directin......from 2 n will reach the surface with same vel oe root2gh n the will go up to height h

 

total time taken to reach height h from for depth h below the surface of water is 2 root 2h/g..................4

 

from 3 n 4

 

total time taken is 4 root 2h/g