The speed of the tennis ball is [tex]8\ \dfrac {km}{h}[/tex] when Alana throws the ball behind at the speed of [tex]11\ \dfrac{km}{h}[/tex].
What will be the speed of the tennis ball?
The speed will depend upon the point of reference of the Alana. As the frame of the reference changes the speed of the ball also changes.
If Alana will throw the ball in the front direction, The speed will be the sum of Alana"s speed and the speed of the ball by which it is thrown.
[tex]19+11=30\ \dfrac{km}{h}[/tex]
If Alana is just leaving the ball without any effort the speed
[tex]19+(-19)=0\ \dfrac{km}{h}[/tex]
If Alana throws the ball behind her at the speed of 19 km/h. The speed of the ball for a sidewalk observer,
[tex]19+(-11)=\ 8 \ \dfrac{km}{h}[/tex]
Thus the speed of the tennis ball is [tex]8\ \dfrac {km}{h}[/tex] when Alana throws the ball behind at the speed of [tex]11\ \dfrac{km}{h}[/tex].
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