# [Physical Science:] Finding Kinetic Energy

1. Feb 13, 2005

### Jessi

Two homework problems I don't understand. :(

9. An alpha particle travels at 1.6 x 10^7 m/s. The kinetic energy of the particle is 6.0 x 10^-13 J. What is the mass of the alpha particle?

I think scientific notation is supposed to be used, so "1.6 x 10^7" is 16,000,000 and "6.0 x 10^-13" is .0000000000006, but I still don't know what to do with the numbers.

10. An electron with a mass of 9.0 x 10^-31 kg moves through a vacuum with a speed of 2.5 x 10^8 m/s. Find the electron's kinetic energy.

Again, I'm guessing "9.0 x 10^-31" is .0000000000000000000000000000009 and "2.5 x 10^8" is 250000000, so does that make the answer 2.8125 x 10^-14

2. Feb 13, 2005

### Jameson

Kinetic Energy is found by the equation

K.E. = .5 *m* v^2

where m = mass and v = velocity

3. Feb 13, 2005

### dextercioby

You may wanna use the relativistic formula for the second case,though,it's roughly 83% of the speed of light...

Daniel.

P.S.And yes,please use scientific notation...Nobody will be willing to count the zeros...

4. Feb 13, 2005

### Jessi

I'm given the kinetic energy - how do I find the mass?

Dexter, I'm sorry..I didn't understand anything that you said. I don't think I'm familiar with the relativistic formula. I'm guessing what I did was wrong, then? :P

5. Feb 13, 2005

### dextercioby

Okay,no problem,then don't use it.Use the classical one.Extract mass,knowing the KE and velociy.A mere division...

Daniel.