A child of mass 40kg stands on a stationary skateboard of mass 4kg on a smooth horizontal surface. The child throws a 2kg sandbag horizontally forward so that the bag leaves the child’s hands at 12m/s relative to the ground.
(i) Determine the speed and direction of the child–skateboard combination immediately after the sandbag is released.
(ii) Calculate the kinetic energy gained by the child–skateboard combination and compare it with the kinetic energy gained by the sandbag.
(iii) If a rough patch 1.5m long brings the skateboard to rest uniformly, find the average frictional force exerted by the patch on the skateboard.