Mike throws a ball upward & toward the east at a 20.0 angle with a speed of 51.0 . Nancy drives east past Mike at 15.0 at the instant he releases the ball.

Question

What is the ball's initial angle in Nancy's reference frame?

Answer 1

v(x) = v•cosα = 51•cos20 = 47.9 m/s.
Relative velocity
v(x-rel)= 47.9-15 = 32.9 m/s.
v(y) = v•sin20 =17.4 m/s.
tanφ = v(y)/v(x-rel) = 17.4/32.9 = 0.53.
φ = 27.9º