First slide

Change of state

Question

A piece of ice falls from a height h so that it melts completely. Only one – quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of h is (Latent heat of ice is 3.4 $\times 10^{5}$ J $k g^{- 1}$ and g = 10 N $k g^{- 1}$ )

Moderate

A

34 km
B

544 km
C

136 km
D

68 km

Solution

$\begin{matrix} \frac{1}{4} m g h = m L \Rightarrow h = \frac{4 L}{g} = \frac{4 \times 3.4 \times 10^{5}}{10} = 13.6 \times 10^{4} \\ = 136 \times 10^{3} m \\ = 136 km \end{matrix}$

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