Walker, Halliday & Resnick — Center of Mass and Linear Momentum: Problem 60

60 In Fig. 9-56, block $A$ (mass $1.6 \text{ kg}$) slides into block $B$ (mass $2.4 \text{ kg}$), along a frictionless surface. The directions of three velocities before ($i$) and after ($f$) the collision are indicated; the corresponding speeds are $v_{Ai} = 5.5 \text{ m/s}$, $v_{Bi} = 2.5 \text{ m/s}$, and $v_{Bf} = 4.9 \text{ m/s}$. What are the (a) speed and (b) direction (left or right) of velocity $\vec{v}_{Af}$? (c) Is the collision elastic?