when a porter lifts a suitcase and puits it in his head. is the work done by him positive, negative or zero?when the suitcase falls from his head what is the work done by the gravity?

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Solution

Here, the work done by gravity is negative. And also, porter is doing a positive work as the the force applied by him is in the same direction as that of displacement and the work done by porter is stored as the potential energy of the object.
When the suitcase falls down, then the work done
=Force x vertical distance

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