A trolley on a smooth track is pulled eastward by a 60 N force and westward by a 40 N force.
(i) Are the horizontal forces initially balanced or unbalanced?
(ii) A student now adds an extra horizontal force toward the west so that the trolley moves with constant velocity. What should be the magnitude of this added force?
a) (i) Balanced; (ii) 20 N
b) (i) Unbalanced; (ii) 40 N
c) (i) Unbalanced; (ii) 20 N
d) (i) Balanced; (ii) 0 N