Final answer:
To change a ball's speed without affecting its direction, you must apply a force in the same or opposite direction as its motion. The correct answer to the question is option a) Apply a force in the opposite direction of motion. This answer aligns with Newton's first law, which relates to the concept of acceleration.
Step-by-step explanation:
To cause a ball to change its speed but not direction, you must apply a force that is in the same direction as the ball's motion to increase speed, or in the opposite direction of motion to decrease speed. This corresponds to Newton's first law and the concept of acceleration being a change in velocity, where velocity includes both speed and direction. Hence, a change in motion implies a change in speed or direction or both, due to a net external force leading to acceleration.
Given the options provided: a) Apply a force in the opposite direction of motion, b) Change the mass of the ball, c) Alter the surface on which the ball is rolling, d) Adjust the angle at which the ball is thrown, the correct answer is a). Applying a force in the opposite direction of the ball's motion will change its speed without altering its direction, which aligns with Newton's laws of motion.
It is important to note that while options b), c) and d) could influence the ball's motion, they do not directly change the speed without potentially changing its direction as well. Changing the mass of the ball while it is in motion is practically infeasible and would not directly affect its current state of motion unless other forces are involved. Altering the surface could change the frictional forces acting on the ball, affecting both its speed and potentially its direction. Finally, adjusting the angle at which the ball is thrown changes the initial direction of the ball's motion, not its speed at a given moment.