# Constant velocity and work done

1. Jun 29, 2016

### Samia qureshi

• Member advised to use the homework template for posts in the homework sections of PF.
if a body is moving with constant velocity. Its work done will be? in my point of view Work done is change in energy. Constant velocity means no change in energy. So work done is zero am i right?

2. Jun 29, 2016

### Mr-R

Yes, in the absence of fields the work done is equal to the difference of Kinetic energies at two different points: $$W=\Delta KE.$$ Since the velocity is constant, then $$\Delta KE=0.$$

3. Jun 29, 2016

### Samia qureshi

Thank you

4. Jun 29, 2016

### CWatters

Perhaps read up on the Work Energy Theorem. This says that the work done by all forces acting on a particle equals the change in the kinetic energy of the particle. In some cases you have to consider the negative work done by gravity or air resistance.

5. Jun 29, 2016

### Mr-R

I think I should have written in the absence of non-conservative fields :)

6. Jul 2, 2016

thank you :)

7. Jul 4, 2016

### rude man

That still leaves out gravity, if the object is moving partially or wholly in a gravitational field. And gravity is conservative!

8. Jul 4, 2016

### Mr-R

You are absolutely right. The work-energy theorem is true for general forces regardless of them being conservative or not (depends on the resultant force). $$\Sigma W=\Delta KE$$ where $$\Sigma=W_c+W_{nc}$$ Conservative and non conservative, respectively. Is this correct?

9. Jul 5, 2016

### rude man

Yes, although more conventionally we say that the work done on a mass equals the gain in its potential plus kinetic energy. You have essentially conflated p.e. into work but I guess that is OK too.

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