While skateboarding at 19 km/h, Alana throws a tennis ball at 11 km/h to her friend Oliver. If Alana is the reference frame, the speed of the tennis ball is km/h.

Physics · High School · Tue Nov 03 2020

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Here, it is given that frame of reference for this case is Alana.

Thus, tennis ball has a speed relative to the to Alana.

So, the speed relative to Alana is the same speed with which Alana throws the ball.

Hence, speed of tennis ball = 11 km/h