Who will do more work?

Classical Mechanics Level 1

Who will do more work? A person responding to a phone by picking it up or a person failing at pushing a car a distance (He isn't able to move it).

A person failing at pushing a car A person responding to a phone by picking it up

4 solutions

Sravanth C.
Nov 7, 2015

Physics defines work when a force applied on an object displaces it, mathematically, $\text{Work = Force . }\text{displacement} = F . s\\ W = F\times d\cos\theta$

Hence a person who is applying force constantly to an object, but is not able move it(displacement=0) has not done any work. Whereas a person who has lifted a mobile phone displaces the mobile against the force due to gravity, doing some work. Though it sounds awkward in reality, it's physics.

What about the force and displacement of himself? If he pushes and does not move at all then the theory is correct. But if he leans in and pushes himself even slightly backwards trying to push the object is he not doing work?

Jeremy Cleaver - 5 years, 7 months ago

I think that'd be "work is being done on him" if he's the one being displaced by the reaction force (here the reaction force would be the one doing the work). The question however is concerned about "work that is being done by him".

Then again, don't take my word for it (I suck real bad in physics).

Prasun Biswas - 5 years, 7 months ago

The Man who failed to push the car is doing effort or work done and this work done is a function of the car potential energy

Mohamed Abdelmegid - 5 years, 7 months ago

To be precise, work is actually defined as the dot product of the force and displacement vectors.

Prasun Biswas - 5 years, 7 months ago

Exactly, work $=F.s = F\times s \cos\theta$ . Your explanation is right sir, the work was supposed to be done by him but not on him.

Sravanth C. - 5 years, 7 months ago

I was about to write the $\cos \theta$ part. Well you should really edit the answer and make it F.d. $\cos \theta$ .

Satyajit Ghosh - 5 years, 6 months ago

@Satyajit Ghosh – I've edited it. :)

Sravanth C. - 5 years, 6 months ago

Krishna Priya
Nov 9, 2015

There will be more energy used in picking up an object than moving it

I disagree. Any force at all will move an object in space. It would take more energy to pick up a phone on Earth. Also, the actual reason is work=force*displacement, and the displacement of the car was 0.

Brian Wang - 5 years, 6 months ago

That is totally the correct argument I would have given. You should also look at picking up an object as moving it against gravity.

Satyajit Ghosh - 5 years, 6 months ago

Sadasiva Panicker
Nov 21, 2015

Work done = Force x distance; pushing a car with no distance, no work done. But lifting a phone cover a distance, There is work done.

Jeff Kraschinski
Nov 20, 2015

The person with the car is definitely exerting a great deal more force, but the failure to move the car results in less work done.

Who will do more work?

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