To determine the angle between the applied
force and momentum, let us resolve into horizontal and vertical components,
Px=sint and Py=cost
∴ Resultant momentum, P=√Px2+Py2=1
Since, the magnitude of resultant momentum is independent of time, the force must be at right angles to the instantaneous velocity or instantaneous momentum, as in case of circular motion.
So, the correct option is (d).