Question

A brick weighing 4.0 kg is dropped into a 1.0 m deep river from a height of 2.0 m. Assuming that 80% of the gravitational potential energy is finally coverted into thermal energy, find this thermal energy in calorie.

Answer 1

Total P.E = $4\times 10\times 3$ = 120 J

Energy utilized = $120\times \frac{80}{100}$ = 96 J

= $\frac{96}{4.2}$ = 22.857 cal.

$\approx$ 23 cal.