The rear side of a truck is open and a box of mass 20 kg is placed on the truck 4 m away from the open end. The coefficient of friction between the box and the surface is 0.15. The truck starts from rest with an acceleration of 2 m s−2 on a straight road. The box will fall off the truck when it is at a distance from the starting point equal to (take g=10 ms−2)