Question

A body of mass $5\text{kg}$ falls from a height of $30\text{metres}$. If all of its mechanical energy is converted into heat, then heat produced will be
$[\text{Take}g=9.8{\text{m/s}}^2\text{and}J=4.2\text{J/cal}]$

• A. $350\text{J}$
• B. $350\text{cal}$
• C. $375\text{J}$
• D. $375\text{cal}$

Answer 1

The correct option is B $350\text{cal}$

Let us assume,
Work done by gravity is $W$, heat produced is $\left(H\right)$ and mechanical equivalent of heat is $J$.
We know that, Mechanical work done $W=JH$
From the data given in the question, we can write that,
$mgh=J\times H$
$\Rightarrow H=\frac{mgh}{J}=\frac{5\times 9.8\times 30}{4.2}=350\text{cal}$
Thus, option (b) is the correct answer.