Question

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.

Answer 1

the answer is 11km/h .. i just took the test.

Answer 2

When Alana moving 19km/h, a stationary object will be perceived by her as moving toward her with 19km/h velocity. If the object is not stationary(velocity isn't zero), the speed will increase by the object velocity.

the relative speed of the tennis ball=
the speed of Alana + true speed of the tennis ball
19km/h+ 11km/h= 30km/h