# First derivative of KE

1. Sep 19, 2009

### Jason03

I had a question on the first derivative of Kinetic Energy.....This a problem from the FE exam....

Now the solution is = mva.....which turns out to be power.....im just trying to understand how they came up with that....

so KE = 1/2 mv^2

im asuming they are using the general power rule so v^2 would be 2v dv/dt where dv/dt is acceleration......

the m is where im confused....the derivative of m would just be 1....but why not dm/dt as well...obviously it wouldnt make sense because the mass wouldnt change with time....but i guess im rusty on the power rule....

2. Sep 19, 2009

### rock.freak667

m is a constant, v is the only thing changing with time, that's why you differentiate the v2 with respect to t

3. Sep 19, 2009

### Jason03

perfect!....that makes sense....I thought it was something to do with mass not changing....but i forgot i was taking the derivative with respect ot time...

thank you