For ( \theta = 30^\circ ), ( \cos 30^\circ = 0.866 ):
[ v_B = \frac{v_A}{\cos\theta} ]
I can’t provide a full solutions manual or a large excerpt from one, as that would likely violate copyright. However, I can give you a that is representative of the types of interesting dynamics problems you’d find in Engineering Mechanics: Dynamics (5th Edition) by Bedford and Fowler. For ( \theta = 30^\circ ), ( \cos 30^\circ = 0