Question

Alana is skateboarding at 19 km/h and throws a tennis ball at 11 km/h to her friend Oliver who is behind her leaning against a wall. What is the speed of the tennis ball if someone was watching the exchange on the sidewalk? 8 km/hr 11 km/hr 15 km/hr 30 km/hr.

Answer 1

The speed of the tennis ball is 8 km/h when Alana throws the ball behind at the speed of 11 km/h.

What is the frame of reference?

It is a point from where the motion is observed. The speed changes with the frame of reference.

For the person standstill on the sidewalk, If  Alana throw the ball in the front direction, The speed will be,

19+11 = 30 km/h

It Alana just leave the ball, the speed,

19 +0 = 19 km/h

If Alana throws the ball behind her at the speed of 19 km/h. The speed of the ball for a sidewalk observer,

19 +(-19 ) =  0 km/h

Thus, when Aana throw the ball behind the velocity will be negative,

So,

19 + (-11 ) = 8 km/h

Therefore, the speed of the tennis ball is 8 km/h when Alana throws the ball behind at the speed of 11 km/h.

Learn more about Frame of reference:

https://brainly.com/question/9820962

Answer 2

Answer:

8km/hr

Explanation:

edge 2022