Question

A $50kg$ man is running at a speed of $18kmph$. If all the kinetic energy of the man was to be used to increase the temperature of water from ${20}^{\circ }$ to ${30}^{\circ }$. How much water can be heated withis energy?

• A. $5g$
• B. $10g$
• C. $15g$
• D. $20g$

Answer 1

The correct option is C $15g$

Heat energy needed to heat up water by ${10}^{\circ }C=4.2\times 10\times x$

Kinetic energy of the man:

$\frac{1}{2}m{v}^2=\frac{1}{2}\times 50\times (\frac{5}{18}\times 8{)}^2$

$=25\times 25=625$

$625=42\times x$

$x=\frac{625}{42}=14.88=15g$