A solid ball of density half that of water falls freely under gravity from a height of `20 m` and then enters water. Up to what depth will the ball go ? How much time will it take to come again to the wate surface ? Neglect air resistance and viscosity effect in water.

Explanation

`sigma`. Density
`rho` : density of water
`sigma = (rho)/(2)`
`A` to `B` :
`v^2 = u^2 + 2 gh = 0 + 2 xx 10 xx 20`
`v = 20 m//s`
`B` to `C` :
`mg - F_B = ma`
`sigma Vg - rho Vg = sigma Va`
`a = (1 - (rho)/(sigma)) g = (1 - (rho)/(rho//2))g = -g`
Inside water ball moves under retardation `g` The ball moves inside water a distance
`h_0 = h = 20 m`
Time taken by ball to move from `B to C`
`v' = v + at = v - g t`
`0 = 20 - 10t rArr t = 2 s`
Time from `C to B = 2 s`.

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