Understanding the concept of Energy

[tomtomtom1]

Homework Statement

Understanding the concept of Energy

Relevant Equations

Understanding the concept of Energy

Hello all

I am trying to better understand the concept of Energy and i was hoping some could help clear a few things up.

I have a car that is pushing a box with a force of 10N.

The car pushes the box 63 meters as shown below:-

I know that the energy which is the capacity to do work is calculated by the force times the distance, so in this case in would need 630 Joules of energy to move the move with my car.

Given this example would it be correct to say that i will need to burn 630 joules of petrol in order to move this box?
I am trying to connect physical energy such as fire, lighting etc to this number of 630 joules.

Finally, would it be correct to say that in the definition of Energy which is "the capacity to do work", work always relates to a mass being displaced by some distance?

Your thoughts?

Thanks

 

[BvU]

Given this example would it be correct to say that i will need to burn 630 joules of petrol in order to move this box?

Yes, in principle.
Quantities of petrol are not measured in joules, but the conversison can be made.

The efficiency of such a conversion from chemical energy to pushing force is only of the order of a few dozen percent, though. So in practicce a multiple of fuel equivalent to 630 J is needed.

 

[haruspex]

work always relates to a mass being displaced by some distance?

No. It might not require any work, or a force, merely to displace the mass by a distance.
It would require work to accelerate the mass, but you could just accelerate it a tiny amount then wait for however long it takes to travel the distance. You might even be able to recover the work invested when bringing the mass to a halt at its destination.

 

[BvU]

work always relates to a mass being displaced by some distance?

work is also involved in moving a charge in a potential field, compressing or expanding a volume of a gas, emitting light, heating, etc. etc.