Question

The height of waterfall is 84 m. Assuming that the entire kinetic energy of falling water is con-verted into heat, the rise in temperature of the water will be ( g = 10 m$s^{-2}$, J = 4.2 Joule/cal)

• A. ${0.2}^{o}C$
• B. ${1.960}^{o}C$
• C. ${0.96}^{o}C$
• D. ${0.0196}^{o}C$

Answer 1

The correct option is A ${0.2}^{o}C$

Potential energy of m kg of water at 84 m above

$=m10\times 84Joule$

Change in temperature $\Delta T$

$\begin{array}{c}\therefore mc\Delta T=8.40m\\ c\Delta T=840\\ \Delta T=\frac{840}{4200}=\frac{84}{420}={\frac{1}{5}}^{\circ }C\\ ={0.2}^{\circ }C\end{array}$

Option A.