NEET 2021 Physics and Chemistry

Let required height of body is y.
When body from rest falls through height (S – y)
Then under constant accelerationv2=02+2g(S−y)
v=√2g(S−y) ......(1)
When body is at height y above ground. Potential energy of body of mass m
U = mgy
As per given condition kinetic energy, K = 3U

1

2

m(v)2=3×mg(y)

1

2

×m×2g(S−y)=3×mgy (using (1))
S−y=3y
∴y=

S

4

.......(2)
∴v=√2×g(S−

S

4

)=√

3gS

2

.......(3)