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 converted into thermal energy, find this thermal energy in calorie.

Answer 1

Finding potential energy of brick

P.E.$=$mgh

P.E.$=4\times 9.8\times (2+1)$

P.E.$=4\times 9.8\times 3$

P.E. $=117.6$J

According to the question

Thermal energy $=80\%$ of P.E.

$=\frac{80}{100}\times 117.6$

$=94.08$J $=94.08\times 0.239$

$=22.48512$ cal

Thus, thermal energy is $22.48512$ cal.