a man stands hoiding a box above his head for 30 minutes.Is any work done by him?justify.?

Answer 1

As physics defines work, W=E*d, as energy times distance, then no. No NET force is being applied IN the direction of NET displacement (movement). If the box returns to the same position (specifically w.r.t. the direction of the force), then there is NO NET displacement.

As people define work, as the energy expended per time, then yes, because he is consuming energy.

As industry defines work, as productive contributions to the bottom line, then no, because most business don't make a profit by having people hold boxes over their heads for 30 minutes, unless its for entertainment.

Answer 2

What a lot of responses - and I'm sorry to see many people have responded as if the question were 'a robot holds a box over its head for 30 minutes, did it do any work?' and I'm not certain why people who seem to know basic physics more than me have missed this vital common sense point!

No, a robot wouldnt, it would have getting it up there but then you could switch it off and its arms one would presume would stay in the same place without using any energy at all.

HOWEVER a man is not a robot - a man cannot be switched off and frozen in a certain position. His arms will MOVE, the blood moving, the tiny twitches, all will have to be counteracted to keep the box in its position, the tension of the muscles is a form of work but the main point is that there will need to be adjustments as a man cannot perfectly hold a box above his head still. Hope that makes sense.

Answer 3

The only work done by the man on the box would be the lifting of the box to that position. Once the box is being held still above his head, he is no longer doing any work. Work is the applied force over a distance. Since the box is not moving relative to the man, he is doing no work on the box.

Answer 4

Theoretically, he did not, but practically, he might have. As the other respondents have said, Work = Force x Distance. We all agree that when he lifts the box, he does work. But think about it, are his hands rock-steady ? I think everyone's hands shake a little, especially if they have to hold a box above their heads. If the box so much as moves 1/10000th of an inch, he'd have done some work. So I think the likelihood that he did some work is more.

Answer 5

Well this is a very general doubt. and it arises not because of lack of understanding of concept of work but due to that name "work done" has 2 different meanings in 2 different contexts.

So let get it straight, if U take the work done by man as the effort applied by him then the work done is considerable by man.Because man ultimately has to apply some force to keep the box lifted on his head.

But when U consider this U are actually watching the 'force applied" by the man in actual. U say that man did some 'work' because U observe that the man continuously applied some force on his head to lift it.

But in physics terms work done is not the force but the impact of the force. If somebody has applied a force then the work done by that force ( or the agent applying the force )

Since the force applied on the man was not able to change the state of box ( again the state here means the state of motion of the body ) so the 'work done in physics sense is 0 here.

always keep in mind that term work done is used for the force applied in general sense but the IMPACT of that force in the sense of physics.
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Answer 6

There will be work done in moving the box above his head, but there won't be any work done when it is above his head per se, since the box isn't actually travelling anywhere (Work done = Force applied x Displacement).

Some energy will have to be expanded, since he will have to overcome the weight of the box to keep it stationary.

Answer 7

No work is being done.

Since this is the Physics topic, I use the technical Physics definition of work, which is force times distance. Since the box is motionless, the distance is zero and the work is zero. The concept of work in physics is not to be confused with the concept of work in everyday life. In physics, work is energy ADDED to the box, and you don't add energy by just holding it up. In everyday life, work is anything that makes you weary, which is a TOTALLY different concept.

Answer 8

Through the physics standpoint, no. There is no distance being covered. However, that would be assuming gravity is a truly steady and constant force, which it is not believed to be (supposedly it has minute fluctuations), and he, as well, would have to remain a perfectly steady and constant force, which is improbable. So, if he isn't holding it perfectly steady, which is highly probable, then yes. Even the slightest distance covered turns it into work.

Answer 9

No work. In Physics, work done is defined by the product of force applied into the displacement of the body on which force was applied. In this case, the man applies a force of magnitude mg (m is the mass of the box) to counter the force exerted by gravity. But this application of force do not produce any displacement in the body. Hence according to definition of work done, no work is done.

Answer 10

work= Force X Distance

he is exerting a force equal to gravity pushing the box down, but since there is no distance being traveled then there is no work being done.

work would be done getting the box up and over his head but that is all.