### Kinetic Energy vs Power

Posted:

**Sun Apr 29, 2018 11:52 pm**Can 1/2mv^2 and mv be used for the same problem if we're only given kinetic energy or power? Like If we are given power, can we solve for kinetic energy?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=15&t=31239

Page **1** of **1**

Posted: **Sun Apr 29, 2018 11:52 pm**

Can 1/2mv^2 and mv be used for the same problem if we're only given kinetic energy or power? Like If we are given power, can we solve for kinetic energy?

Posted: **Mon Apr 30, 2018 1:05 am**

The P in p=mv stands for momentum. The equation for Power is Force x Velocity. In a case where we are only given momentum, I think we can solve for Kinetic energy ( E=threshhold+KE ) if we substitute other equations for E and get it in terms of p=mv

E = threshold + KE

hv = threshold + KE

KE = hv - threshold ----> substituted Energy per photon equation (E=hv)

KE = h(c/λ) - threshhold ----> substituted Speed of Light equation ( nu=c/λ)

KE = h(c/(h/p)) - threshhold ----> substituted DeBroglie's equation (λ=h/p)

KE = hcp/h - threshhold

KE = cp - threshold -------> simplified

KE = c(mv) - threshhold ----> all that's left is the speed of light constant and momentum which is pretty good if we're only given p

I don't know if this is right or if it answers your question, but it makes sense to me right now haha

E = threshold + KE

hv = threshold + KE

KE = hv - threshold ----> substituted Energy per photon equation (E=hv)

KE = h(c/λ) - threshhold ----> substituted Speed of Light equation ( nu=c/λ)

KE = h(c/(h/p)) - threshhold ----> substituted DeBroglie's equation (λ=h/p)

KE = hcp/h - threshhold

KE = cp - threshold -------> simplified

KE = c(mv) - threshhold ----> all that's left is the speed of light constant and momentum which is pretty good if we're only given p

I don't know if this is right or if it answers your question, but it makes sense to me right now haha

Posted: **Fri Oct 12, 2018 2:15 pm**

Along with the previous response, I think to answer your question, you can solve if given power, but you'd also need to be given the force, or be able to solve for force with outside information. I'm not sure if we'd ever get a question like that or not though because that treads more into a physics question for a lot of it rather than just general chemistry.