Question

please solve the above question whose answer is 4 h

Answer 1

I and II represents the first and second case. Hope its helpful

Answer 2

the body is falling freely under gravity, so the gravitational acceleration= a = g
the initial velocity of the body = u = 0
After covering distance h 
the velocity becomes v

so v²-u² = 2gh
or v² = 2gh
after some time(t) its velocity doubles = v' = 2v
let the distance covered in time t = h
Here the initial velocity = v 
so, v'² - v² = 2gh'
(2v)²-v² = 2gh
4v²-v²=2gh'
3v² = 2gh
3(2gh) = 2gh' (∵ v² = 2gh given above)
3h' = h
thus, h is 3 times h.