A streamlined body falls through air from a height $h$ on the surface of a liquid. If $d$ and $D(D > d) $ represents the densities of the material of the body and liquid respectively, then the time after which the body will be instantaneously at rest, is
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(d) Upthrust -weight of body = apparent weight
$VDg - Vdg = Vda,$
Where $ a = $ retardation of body
$VDg - Vdg = Vda,$
Where $ a = $ retardation of body
$a = \left( {\frac{{D - d}}{d}} \right)\;g$
The velocity gained after fall from $ h$ height in air, $v = \sqrt {2gh} $
Hence, time to come in rest,
$t = \frac{v}{a} = \frac{{\sqrt {2gh} \times d}}{{(D - d)g}} = \sqrt {\frac{{2h}}{g}} \times \frac{d}{{(D - d)}}$
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