A stone of mass 0.5 kg is to be raised from the ground to a balcony that is 4 m above the ground.
(a) Calculate the work done by the gravitational force when the stone is lifted vertically upward at constant speed.
(b) The same stone is carried up an ideal (smooth) inclined plank 5 m long that reaches the same balcony height of 4 m. Find the work done by the gravitational force during this motion.
(c) Compare your answers of parts (a) and (b) and state what this reveals about the nature of the gravitational force.