# Homework Help: Work and energy

1. Nov 2, 2006

### moomoocow

hi!

can i say that
when work is done, it is equal to potential energy, which is equal to kinetic energy?

can somebody please correct me if i misunderstood it?

Last edited: Nov 2, 2006
2. Nov 2, 2006

### semc

nah u cant say that.basically u cant even say PE is equal to KE its the change that is equal

3. Nov 2, 2006

### stunner5000pt

when work is done energy is converted from one form to the other

the potentail energy may not necssarily equal the kinetic energy... what if there was friction or some other external force?

4. Nov 2, 2006

### moomoocow

oo
so its the loss of potential energy which is equal to KE?

5. Nov 2, 2006

### stunner5000pt

this is not always true

think of this:

suppose there was box on top of a hill. And the surface of the hill had friction. Then as the box slides down the hill what can you say about the kinetic energy gained by this box? Is it equal to the potnetial energy lost? Wh or Why not??

6. Nov 2, 2006

### semc

suppose u push a box on a frictionless surface, PE wrt the floor will always be zero but there is still some KE