Initial velocity u = 20 m/s; m = 1 kg Kinetic energy = maximum potential energy Initial kinetic energy =
1
2
×1×202=200J mgh(max)=200J ∴h=20m The height travelled by the body,h'=18m ∴ Loss of energy due to air friction =mgh−mgh′ ⇒ Energy lost =200J−1×10×18J=20J