Question

A body of mass 5 kg falls from a height of 30 M if its all mechanical energy is changed into heat then heat produced will be

Answer 1

m=5 kg ,h=30
since ball is dropped therefore u=0
now v^2-u^2=2*g*h
v^2-0^2=2*9.8*30
v^2=588 m/s since mechanical energy is converted into heat energy therefore
mechanical energy = kinetic energy = heat energy
heat energy = (1/2)*m*(v^2) =1/2*5*588= 1470 joule
Heat = 1470/4.2
=350 Cal.

Method 2

W=JQ

mgh=J×Q

Q=mgh/J=5×9.8×30/4.2=350 Cal

Simple energy conservation