Respuesta :
Haven't taken physics but I would assume if her friend is standing in front of her that you would add up the speeds and get 30 km/hr.
Answer : Speed of tennis ball is 30 km/h.
Explanation :
Alana's speed on the skateboard is 19 km/h
She throws a tennis ball at 11 km/h
Alana is throwing a ball towards her friend Oliver.
That means the velocity of Alana and ball gets added up.
So, Speed of tennis ball is [tex]v_t=19\ km/h+11\ km/h=30\ km/h[/tex]
