Candidates were expected to recall that force = mass x acceleration. They were expected to obtain the acceleration from the position vectorr = (4t3 - t2) i - (2( -t) j by finding the second derivative of r with respect to t to obtain dZzT = (24t - 2)i - 4j . At t = 2, dZzT = (24(2) - 2)i - 4j which gave 46i - 4j.
                     dt                                                 dt
Thus, r = ma = 3(46i - 4j) = 138i -12j.

Majority of the candidates were reported to have performed poorly in this question which the report attributed to their inability to recall the relation: force = mass x acceleration ( f = ma).