# Why does a moving object gain energy?

1. Jan 27, 2016

### ppppparker

1. The problem statement, all variables and given/known data
One of the hints to this problem says "An object in motion always gains kinetic energy, so the change in energy of an object starting from rest would be P = m(v^2) / (2t)

I understand that a moving object has kinetic energy, but why did they say it gains kinetic energy (or maybe im not understanding grammar?) thanks for any help

2. Relevant equations
KE = (1/2) m(v^2)

3. The attempt at a solution

2. Jan 27, 2016

### SteamKing

Staff Emeritus
An object can gain KE only if m or v or both increase. If m = constant and v = constant, then KE must be a constant.

3. Jan 27, 2016

### CWatters

That's not quite correct. P in that equation appears to stand for Power which is the rate of change of KE.

If the object starts at rest and some time t later has velocity V then the change in KE is...

∆KE= m(v^2)/2

4. Jan 27, 2016

### CWatters

They say it gains KE because it started from rest KE=0 and ended up with velocity V and KE=m(v^2)/2.

5. Jan 27, 2016

### CWatters

That's not true. An object moving with constant velocity does not gain KE. It's KE stays the same. Objects only gain KE if the velocity increases.

Are you translating this from another language?

6. Jan 29, 2016

### ppppparker

thats exactly what ive been thinking for a number of questions actually.. the grammar is messing up the questions so i think it must be translated .. but its on Khan academy , kinda surprised me cuz I thought Khan is a pretty serious site now..

7. Jan 29, 2016

### Staff: Mentor

Perhaps it meant to say, "An object set in motion always ...."

8. Jan 29, 2016

### Merlin3189

Could you post a link? I can't find that sentence in the likely sections I've looked through.