we know that the total energy of a body remains conserved......so initial energy = final energy.......initially we will only have kinetic energy and zero potential energy.....at some height the KE becomes half along with some potential energy,,,,,,, ...KE = 0.5KE + PE... ...0.5KE = MgH... ...0.25 x M x V x V = M x g x H...initial velocity V = 4m/s... ...0.25 x 16 = 10 x H... ...H = 0.4 metres