The velocity of a body of mass 20 kg decreases from 20 m/s to 5 m/s in a distance of 100 m. Force on the body is:

Here initial velocity is u=20 m/s and final velocity is  5 m/s and distance travelled is 100 m. Then from the equationv2-u2=2as  ; 52-202=2a×100 a=-25×152×100 and F=ma=-20×25×152×100=-37.5N