# Recent content by darkblue

1. ### Representing a Cardioid

Homework Statement Show that the cardioid r=a(1+cos(theta)) can be represented by r=2acos2(theta/2), 0<=theta<=2pi (theta is between 0 and 2pi). Homework Equations The Attempt at a Solution I'm pretty sure I have to equate the two expressions, but I haven't been able to do this...
2. ### Electric Potential Energy of a System of Charges

Oh I see...that makes sense. You're right, I was counting each interaction twice. I worked on the problem again and got (4+sqrt(2))kQ2/a...can anyone confirm this?
3. ### Electric Potential Energy of a System of Charges

Woops sorry, the line that says U = (8+sqrt(8)kQ2)/a is supposed to say: U = ((8+sqrt(8))kQ2)/a
4. ### Electric Potential Energy of a System of Charges

Homework Statement A square of side a has a charge +Q at each corner. What is the electric potential energy of this system of charges? Express your answer in terms of the variables a, Q and appropriate constants. Homework Equations U=kq1q2/r The Attempt at a Solution I figured...
5. ### Energy Conservation - Electric Potential Energy

Oh I see...my calculator didn't show me those last few digits. Thanks so much for your help!
6. ### Energy Conservation - Electric Potential Energy

I don't quite understand what I've done wrong. I did the calculation again and I'm still getting 7.0x10^-9 C. I'm assuming the units of C are correct since the division yields Joules/Volt, and Joule = Coulomb * Volt. I also checked over my conversion of MV to V and that is correct as well.
7. ### Energy Conservation - Electric Potential Energy

Homework Statement In proton-beam therapy, a high-energy beam of protons is fired at a tumor. The protons come to rest in the tumor, depositing their kinetic energy and breaking apart the tumor’s DNA, thus killing its cells. For one patient, it is desired that 0.10 J of proton energy be...
8. ### Setting up an Integral for the area of a surface of revolution

oops, i meant to put a "*" for multiplication. Thanks for your help!
9. ### Setting up an Integral for the area of a surface of revolution

So does this mean that the way I have set it up is correct? I had a feeling it wasn't right because I couldn't see what steps I'd take next in the event that I had to solve it.
10. ### Setting up an Integral for the area of a surface of revolution

Homework Statement Set up, but do not evaluate, an integral for the area of the surface obtained by rotating the curve y=xe-x 1=<x=<3 about the y-axis. Homework Equations S=integral from a to b x 2pix ds where ds=sqrt(1+(dy/dx)2)dx The Attempt at a Solution The first thing I...
11. ### Walking away from two loudspeakers-destructive interference

Thanks for all the help! :)
12. ### Walking away from two loudspeakers-destructive interference

I just thought of something...would I use n=1 and then n=0 to find the other 2 values?
13. ### Walking away from two loudspeakers-destructive interference

Ok, I solved it the way you said and everything worked out :) The only problem is that they're asking for three values...how would I find the other 2?
14. ### Walking away from two loudspeakers-destructive interference

I see. So now I'm trying to solve for the distance...I tried doing this by first solving for the path difference by using L1-L2=(n+1/2)lambda, since we know n=2 and lambda=0.5. When I did this, I got the path difference as 1.25. I am now trying to solve for L2 (the distance from the speaker you...
15. ### Walking away from two loudspeakers-destructive interference

I think I understand what you're saying...n should be 2, right?