First slide

Calorie

Question

From what height a piece of ice at zero degree fall in order that it may melt on reaching the ground, assuming no loss of energy on the way : (J = 4.2 J / cal)

Easy

A

3.4 x 10⁶ cm
B

3.4 x 10⁵ cm
C

3.4 x 10⁶ mts
D

3.4 x 10⁵ cms

Solution

Let m be mass of ice block and h be the height above the ground.
$∴$ Work done W = mgh.
Heat produced $Q = \frac{W}{J} = \frac{mgh}{J}$
Heat required to melt ice block Q’ = mL
$\begin{array}{l} ∴ \frac{mgh}{J} = mL \\ h = \frac{JL}{g} = \frac{4 .2 \times 80 \times 10^{3}}{9 .8} \\ = 3 .4 \times 10^{4} m = 3 .4 \times 10^{6} cm \end{array}$

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