Posted by **Cory** on Sunday, October 31, 2010 at 3:29pm.

Sorry for re-posting but I really need to know if I did it right. Please someone help!

Two 3.0g bullets are fired with speeds of 40.0 m/s and 80.0 m/s respectively. What are their kinetic energies? Which bullet has more kinetic energy? What is the ratio of their kinetic energies?

I got 60 for the first bullet and 120 for the second. I am not sure I used the formula correctly and I do not know how to obtain the "ratio" for kinetic energies. I would appreciate any help

- Physics( Checking answer) -
**T**, Monday, November 1, 2010 at 2:13pm
The first bullet has 2.4 Joules of energy, and the second has 9.6 Joules of energy. The equation is 1/2*m*v^2: You forgot that the mass is given in grams instead of kilograms, so you need to convert to kg (grams/1000, so .003 kg). You also didn't square the velocities. The ratio would just tell you how much more the kinetic energy of the second is compared to the first (KE1/KE2): here, it comes out to be 1/4 (which is also the quotient of the velocities squared).

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