Water in a tank has been freezed completely. The height of freezed water is $H$. When the entire ice

Question

Water in a tank has been freezed completely. The height of freezed water is $H$. When the entire ice gets melted, the work done by gravity is (Take $\left.\frac{	ext { density of ice }}{	ext { density of water }}=0.9ight)$

Professor PC Thomas Classes · Answer

$H$ height of freezed water becomes $0.9 H$ height of liquid water on melting. Thus,\ 
$U_i=m g \frac{H}{2}=0.5 m g H$
$U_f=m g\left(\frac{0.9 H}{2}ight)=0.45 m g H$
$W_g=U_i-U_f=0.5 m g H-0.45 m g\ H\=0.05 m g H$