I) Newton's First Law of Motion states that ball I, being stationary, will remain at rest unless an unbalanced external force acts upon it. This implies that the net external force acting on ball I

i) Newton's First Law of Motion states that ball I, being stationary, will remain at rest unless an unbalanced external force acts upon it. This implies that the net external force acting on ball I is zero.

ii) Two possible effects of external forces on ball I:

• It could start to move (accelerate from rest).
• It could change its shape (deform).

iii) Newton's First Law of Motion states that ball II, being in motion, will continue to roll at a constant speed in the same direction unless an unbalanced external force acts upon it. This implies that the net external force acting on ball II is zero for it to maintain its current state of motion.

iv) Two possible effects of external forces on ball II:

• It could speed up or slow down.
• It could change its direction of motion.