"A 10.0 g marble slides to the left with a velocity of magnitude 0.600 m/s on the frictionless, horizontal surface of an icy, New York sidewalk and has a head-on elastic collision with a larger 25.0 g marble sliding to the right with a velocity of magnitude 0.250 m/s (Fig. 8.35)."(adsbygoogle = window.adsbygoogle || []).push({});

I need to "Calculate the change in kinetic energy (that is, the kinetic energy after the collision minus the kinetic energy before the collision) for each marble."

So, I will start with the 25g marble going right, which hits the 10g marble and revserses direction to go left

I correctly found the velocity of the 25g marble after the collision, it is -.24.

Now, to find the change in kinetic energy, i did this:

v1=intial velocity

K2-K1=.5mv^2 - .5mv1^2

.5(.025)(-.24)^2 - .5(.025)(.25)^2

isn't this how one is supposed to find change in kinetic energy? Then why is it incorrect? did i go wrong with the positive negative sign?

this one should be negative right?

thankyou

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Momentum question, seems easy, y can't I get it

**Physics Forums | Science Articles, Homework Help, Discussion**