TE 7.9

The youngster's speed increases from 2 m/s to 3 m/s, which means that her kinetic energy increases. Thus the change in her kinetic energy is positive. Work - kinetic energy theorem states that the change in kinetic energy of an object is equal to the net work done on the object. Since the youngster's change in kinetic energy is positive, it means that the work done by the force was positive.