The driver provides a constant force on the engine through the foot pedal. Eventually the van stops accelerating and reaches a constant speed. c Explain why the van reaches a constant speed if the driver provides a constant driving force to the van.

It follows from Newton's second law that there is some counteractive force that cancels out the force exerted by the engine - it's most likely drag due to air resistance in combination with static friction between the tires and the road. The car is moving at constant speed past a certain point, so the net force on the car is

∑ F = (force from engine) - (resistive forces) = 0

grav force prop 1/r squared 2r all squared is 4rsquared 1/4rsquared quartered