Basim’s robotics team builds a robot that travels at 9 meters per second and can fire a tennis ball at a target. Which would result in a judge who is sitting beside the testing ground observing the tennis ball having a speed of 7 meters per second ?

The judge measures the ball’s speed relative to the ground. When the robot fires backward, the ball’s velocity relative to the ground is the robot’s 9 m/s forward speed minus the ball’s backward firing speed. Firing backward at 2 m/s gives 9 − 2 = 7 m/s, so choice D is correct. Firing backward at 7 m/s would make the ball’s ground speed only 2 m/s.

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