Candidates were expected to recall that force = mass x acceleration. They were
expected to obtain the acceleration from the position vector*r *= (4t3 - t2) *i *- (2( -t) *j *by finding the second derivative of *r *with respect to t to
obtain __dZ____z____T__ = (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).