In an elastic collision between two bodies of mass m1 and m2, with m2 initially at rest, mass 1 moves off at angle q relative to the direction of its initial velocity and mass 2 at angle f. an exam paper shows the equations below:
m1v1i= m1v1fcosq + m2v2fsinf
0 = m1v1fsinq + m2v2fcosf
what error(s) has the student made?

a. in the first equation, m_2v_2f sin/should be m_2v_2fcosf.
b. in the second equation, m_2v_2fcos f should bem_2v_2fsinf.
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.

Aperson gives a shopping cart an initial push along a horizontal floor to get it moving, and then lets go. the cart travels forward along the floor, gradually slowing as it moves. consider the horizontal force(s) on the cart while it is moving forward and slowing. which of the following statements is correct? (a) both a forward and a backward force are acting on the cart, but the forward force is larger. (b) only a forward force is acting which diminishes with time. (c) both a forward and a backward force are acting on the cart, but the backward force is larger. (d) only a backward force is acting, no forward force.