# Homework Help: I need help badly

1. Mar 14, 2007

### ryoung815

Velocity Problem - I need help badly!!

Using Niel Bohr's model of the hydrogen atom, the electron travels around the proton in a uniform circular path. Using Newton's 2d law of motion, find an expression for the velocity of the electron and calculate it. The mass of an electron is 9.10 x 10^-31 kg.

I know Newton's 2nd law of motion is f=ma, but how is that applicable?? Help Please!!!:surprised

Thanks,
Ryan

Last edited: Mar 14, 2007
2. Mar 14, 2007

### G01

HINT: When you have circular motion, what is the expression for acceleration?

3. Mar 14, 2007

### ryoung815

acceleration would be 0 if something is moving in a circular motion at uniform speed?

4. Mar 14, 2007

### G01

Uniform SPEED, does not mean uniform VELOCITY! Check the circular motion section of your physics text for the acceleration of an object in uniform circular motion. Then use that as your acceleration.

5. Mar 14, 2007

### leright

no, an object in circular motion has a centripetal acceleration. The fact that the direction of the velocity is changing means that the electron is accelerating, even if its speed is constant.

centripetal acceleration is v^2/R, right? Centripetal force is then mv^2/r.

You can determine the centripetal force also by using coulomb's law, which is kq1q1/r^2, right?

so, kq1q2/r^2 = mv^2/R. you know everything except for the velocity. you know the charge of the electron, you know the charge of the nucleus, you know the bohr radius, and you know the mass of an electron. You can easily solve for v.

6. Mar 14, 2007

### ryoung815

thanks!! I got it. i appreciate the help friends!

7. Mar 14, 2007

### G01

That's awesome! Good Luck to you in the future!