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  4. An ice block at 0° C is dropped from height 'h' above the ground. What should be the value of ' h ' so that it melts completely by the time it reaches the bottom assuming the loss of whole gravitational potential energy is used as heat by the ice? [Given: .Lf=80 cal / gm ]

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Q. An ice block at $0^{\circ} C$ is dropped from height 'h' above the ground. What should be the value of ' $h$ ' so that it melts completely by the time it reaches the bottom assuming the loss of whole gravitational potential energy is used as heat by the ice? [Given: $\left .L_{f}=80\, cal / gm \right]$

Thermal Properties of Matter

Solution:

Applying energy conservation :
$m g h=m L_{f}$
$\Rightarrow h=\frac{L_{f}}{g}=\frac{80\, cal / gm }{10\, m / s ^{2}}$
$=\frac{80 \times 4.2 \times 1000\, J / kg }{10\, m / s ^{2}}$
$\left(\frac{336 \times 10^{3}}{10}\right) \frac{ N - s ^{2}}{ kg }$
$=33.6\, km .$