Final answer:
The direction of drag force on a tennis ball that goes straight up and then comes back down is up and then down, as it opposes the motion during both ascent and descent.
Step-by-step explanation:
The question is asking about the direction of the drag force on a tennis ball that is hit straight up and then comes down. The correct answer to this question is B. Up and then down. When the tennis ball is moving upwards, the drag force acts in the opposite direction to the motion and is therefore directed downwards. Once the ball reaches its peak and starts to fall, the drag force continues to act in the opposite direction to the motion, which in this case is upwards. It's important to note that the drag force always opposes the relative motion of the object through the air.