A porter pushes a trolley on a smooth floor and then pulls it back to his starting point.
Answer the following questions about the work done in each stage of the motion.
(i) Explain what is meant by positive work, negative work and zero work with reference to the directions of force and displacement.
(ii) The porter exerts a horizontal force of 120N on the trolley while moving it 8m forward. State whether the work done in this stage is positive, negative or zero and give a reason.
(iii) While returning, he pulls the trolley with the same magnitude of force through the same distance along the same straight line but in the reverse direction. State the sign of the work done in this stage and justify your answer.
(iv) Calculate the numerical value of the total work done by the porter for the complete to-and-fro trip.