# Kinetic Energy and Work

1. Jun 5, 2006

### miloko

Does the following statement makes sense?

The work in joules required to stop a particle moving with kinetic energy 10 J is, in fact, 10 J if we ignore energy dissipation due to friction.

Thanks,
Mike

2. Jun 5, 2006

### Hootenanny

Staff Emeritus
The highlighted bit is troubling me. It suggests that if we were to consider the energy disappated by friction more than 10J of work we be done, why would this be the case?

The bottom line is that if a particle has x joules of kinetic energy, it requires x joules of work to be stopped.

3. Jun 5, 2006

### Staff: Mentor

...or less. In reality, either way you look at it, it is 10J altogether.

4. Jun 6, 2006

### Dr.Brain

Perhaps work-energy principle states that 'Change in K.E is infact the net work done" , this can be the summation of work done by different sources , or maybe work done by one single source.So to stop the particle , final K.E would be zero , and Work done would be equal to initial K.E ,

Now there might be a case, which you havent mentioned , if the particle is going up the hill , that is gaining P.E while losing K.E , so this time work is being done by gravity to slow it down , there might be a case , that you are pushing the object , while it is going uphill , and also rise in P.E is also helping it ...so net work done is still change in K.E , but this work is being done by you as well as gravity!...