Sat March 12, 2011 By: Rohan Mehra

When collie caries some weight from one place to another why is work done by him zero.He does work in moving.He applies force on the ground and moves.So work should be done.Also more the weight he carries more the force is required so more should be the work done.

Expert Reply
Sat March 12, 2011
Dear student,
Work is zero if Cos θ is zero or θ = Π/2. this explains why no work is done by the porter in carrying the load. As the porter carries the load by lifting it upwards and the moving forward it is obvious the angle between the force applied by the porter and the displacement is 90o.
Physical work and physics work done are different. 
Hope this helps.
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