# Homework Help: HELP, 2 AP physics 1994 problems. Magnetic fields

1. Mar 27, 2009

### skyline_2k7

ok guys so i have two questions, i need help on two questions on the following site "[URL [Broken]

/AP%20Physics%20Daily%20Problems/AP%20Daily%20Prob%20131-140.pdf"]http://staff.hartdistrict.org/glyle/ap_physics/Homework [Broken]/AP%20Physics%20Daily%20Problems/AP%20Daily%20Prob%20131-140.pdf[/URL]

they are questions #133 and 138.

please show me how to get the answers, because my head is hurting from trying to solve these questions.

thanks

Last edited by a moderator: May 4, 2017
2. Mar 28, 2009

### skyline_2k7

ok i just found out that the link doesnt work, so i did a print screen of the pictures of the problems.

if you guys could answer these two i would appreciate it very much.

thanks

Last edited: Mar 28, 2009
3. Mar 29, 2009

### Lambduh

Read the forums rules. Make an attempt at the problem then people will be more than willing to help you :)

4. Mar 29, 2009

### Redbelly98

Staff Emeritus
skyline, welcome to PF.

If it helps, here are the forum rules Lambduh is referring to:

So if you can think about it and tell us something you know about solving the problems, we can offer hints and steer you in the right direction.

5. Mar 29, 2009

### skyline_2k7

ok so

a)im pretty sure that potential difference is the voltage, but i dont know of an equation that has the variables a and V in them. so im stuck there.

b) i think that you might need to set 1/2 m v^2 equal to something else but i dont know that equation either, but you do know the mass of a proton and the velocity is given to you.

c)i think that this is the equation r= mv/qb and just plug everything in and solve for B.

d) im pretty sure its negative Z, into the the page because of the right hand rule.

and for the next problem i have absolutely no clue whatsoever :(

6. Mar 29, 2009

### Redbelly98

Staff Emeritus
Okay, let's work out the first 2 parts first.

Yes, potential difference is the voltage. And voltage (by definition) is the ratio of energy/charge.

So if you knew the kinetic energy gained by each proton, as well as the charge on each proton, you could figure out the voltage.

That's a decent start. Since the proton beam is stopped by the target, all the kinetic energy of each proton will be converted to heat in the target. Note that heat has units of energy, so it is a direct conversion,
kinetic energy → heat energy​

See if you can get those first 2 for now ... or ask for more clarification if you can't.

Regards,

RB