A block of mass $100\, gm$ slides on a rough horizontal surface. If the speed of the block decreases from $10 \,m/s$ to $5\, m/s,$ the thermal energy developed in the process is…………. $J$

A piece of metal of mass $5\ kg$ and temperature $-50\ ^oC$ is dropped in $20\  kg$ water at $52\ ^oC$ temperature. In thermal equilibrium temperature of water decreases by $2\ ^oC$, then specific heat of metal is …… $ Cal/g\,^oC$

A $10\, kW$ drilling machine is used to drill a bore in a small aluminium block of mass $8.0\, kg .$ How much is the rise in temperature of the block in 2.5 minutes, assuming $50\, \%$ of power is used up in heating the machine itself or lost to the surroundings. Specific heat of aluminium $=0.91\,J\,g^{-1}\,K^{-1}$ 

Why the land of desert gets hotter in day time and colder in night time quickly ?

The mechanical equivalent of heat $J$ is