A piece of ice falls from a height  h so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of his [latent heat of ice is 3.4×105J/kg and g=10 N/kg]

Gravitational potential energy of a piece of ice at a height (h)=m g h Heat absorbed by the ice to melt completely ΔQ=14mgh.......(1) Also, ΔQ=mL.......(2) From eqns. (1) and (2), mL=14mgh  or,  h=4Lg Here L=3.4×105 J kg-1,g=10 N kg-1∴  h=4×3.4×10510=4×34×103=136 km