a student goes home in weekend. he lifts his 10kg bag 1m high, and walks 1250m to the station and puts his bag down. The station and his studio are on the same ground level. How much work does he do?
a.0J b.10J c.20J d.1251J

Question

a student goes home in weekend. he lifts his 10kg bag 1m high, and walks 1250m to the station and puts his bag down. The station and his studio are on the same ground level. How much work does he do?
a.0J b.10J c.20J d.1251J

anonymous · Answer

@ajprincess @rajathsbhat @Taufique @Tushara

anonymous · Answer

Perhaps I'm wrong here, but I would think it's 0J... The total work would be picking up the bag, and then putting it back down. The distance is irrelevant here. So the work you do to get the bag 1 meter in the air is given back when you put it 1 meter down. Makes sense?

anonymous · Answer

Total work is zero. Reasoning: to lift the bag he delivers energy to the system to increase the bag potential energy, then he moves 1250 meters but  gravitational force is perpendicular to the trajectory therefore the scalar product is null and the energy is zero and finally the energy is delivered back by the system when he drops the bag, cancelling the initial energy. Result is zero.
Another explanation is that gravitational field is conservative, therefore the energy is the final energy minus the initial energy. So if the bag is on the ground in the beginning and in the end, then the potential energy in these two points is the same and the difference is zero

anonymous · Answer

by the way, Energy and Work are equivalent

anonymous · Answer

thank you! :)