In an Elastic Collision Between Two Bodies of Mass M1 $\theta$

Multiple Choice

In an elastic collision between two bodies of mass m1 and m², with m² initially at rest, mass 1 moves off at angle $\theta$ relative to the direction of its initial velocity and mass 2 at angle $\phi$ . An exam paper shows the equations below: m1v1i
0
= m1v1f cos $\theta$ + m²v2f sin $\phi$
= m1v1f sin $\theta$ + m²v2f cos $\phi$
What error(s) has the student made?

A) In the first equation, m²v2f sin $\phi$ should be m²v2f cos $\phi$ .
B) In the second equation, m²v2f cos $\phi$ should be m²v2f sin $\phi$ .
C) In the second equation, the plus sign between the terms on the right should be a minus sign.
D) All of the errors listed above.
E) Only errors (a) and (b) above.