## calculusxy one year ago MEDAL!!!! If i'm driving in a car at 30kph and a friend is driving in a car with the same mass at 60kph, my friend's car's kinetic energy is bigger than mine by a factor of what? (that is, divide my friend's over mine.)

1. calculusxy

@jim_thompson5910

2. jim_thompson5910

Hint: Kinetic Energy (KE) KE = (1/2)*m*v^2 m = mass v = velocity

3. calculusxy

well since it said that the masses are the same, it would eventually cancel out. however, the velocity would be different because one is going 60 kph and the other is going 30 kph. thus, would i do: $\frac{ 60^2 }{ 30^2 } = \frac{ 3600 }{ 900 } = 4 ?$

4. jim_thompson5910

correct, the friend has 4 times more KE

5. calculusxy

i just wanted to make sure what the units would be.

6. calculusxy

would it just be J , like 4J

7. jim_thompson5910

The joule units would cancel though

8. calculusxy

only 4 right?

9. jim_thompson5910

example: your car m = 100 v = 30 friends car m = 100 v = 60 ------------------------------------------------------- Your KE KE = (1/2)*m*v^2 KE = (1/2)*100*30^2 K = 45,000 Friends KE KE = (1/2)*m*v^2 KE = (1/2)*100*60^2 K = 180,000 Ratio of the two KE values 180,000/45,000 = 4 whatever the units for the KE were, they cancel out when you divide

10. jim_thompson5910

yeah only 4

11. calculusxy

okay thanks :)

12. jim_thompson5910

np

13. calculusxy

so there is also another question on the difference on potential and kinetic energy

14. calculusxy

@jim_thompson5910

15. calculusxy

i wrote: "potential energy is the amount of energy in an object when it is still and at a certain position, however, kinetic energy is when you're calculating the amount of energy of an object when it is moving."

16. calculusxy

will that be fine?

17. jim_thompson5910

potential energy (PE) is the amount of stored energy that can be used and converted into KE example: pick up a rock and place it on a ledge. It has PE stored up. When you push it off the ledge, it speeds up and hits the ground converting that PE into KE

18. jim_thompson5910

potential energy due to gravity PE = m*g*h