A ball whose density is 0.4 × 103 kg/m3 falls into water from a height of 9 cm . To what depth does the ball sink

The velocity of ball before entering the water surface  v=2gh=2g×9When ball enters into water, due to upthrust of water the velocity of ball decreases (or retarded)The retardation, a =  apparent weightmass of ball=V(ρ−σ)gVρ=ρ−σρg=0.4−10.4×g=−32g    If h be the depth upto which ball sink, then, 0−v2=2×−32g×h⇒2g×9=3gh ∴ h=6 cm