# Recent content by ChEJosh

1. ### Biochem practice exam help - Test tomorrow

Hi all. I have a biochem test tomorrow, and would like some help. I went through the practice exam that was given to us, and from past experience the real test and practice test tend to be very similar. Also, from past experience, I tend to get a couple of them wrong because I believe that I...

Bump?
3. ### Linear Algebra: 4 Fundamental Subspaces

Homework Statement Without computing A, find the bases for the 4 fundamental subspaces. [1 0 0][1 2 3 4] [6 1 0][0 1 2 3]=A=LU [9 8 1][0 0 1 2] Homework Equations N/A The Attempt at a Solution There was an "example" in the book. It just showed the answers. It was: [1 0...
4. ### Simple Linear Algebra question

I have to do a LDL^{T} transform of a symmetrical matrix: [2 -1 0] [-1 2 -1] [0 -1 2] And, I'm just wondering if I have to do a row exchange, or something. I can't remember if the L matrix has to have the form [x 0 0] [x x 0] [x x x] where the x's are nonzero numbers...
5. ### Friction: Block on Ramp

So now I get x-direction Fx = N sin() - mu N cos() ax = [N sin() - mu N cos()]/m T = -[v0x cos() m]/[N sin() - mu N cos()] Substitute N = mg cos() T = -[v0x cos() m]/[mg cos() sin() - mu mg cos() cos()] cancel m cos() to arrive at original answer, right? Thanks for all of your...
6. ### Friction: Block on Ramp

How is it the -x-axis? Although, I now see that you're saying that the normal is theta from the positive y-axis, and needs to be sin(theta), right?
7. ### Friction: Block on Ramp

wrt the ramp 90º or wrt x-axis 90º+theta How is the angle not wrt the x-axis? It's the angle made by the ramp with the x-axis
8. ### Friction: Block on Ramp

No? I always thought that if it was an x component it was cosine, and y component was sine. Those are both the x components, so...
9. ### Friction: Block on Ramp

For part a, I got T = -v0/(g sin(theta) - mu g cos(theta)] Obviously since it's the same situation, I should be able to get the same answer for part b, But I'm having difficulty. x-direction Fx = N cos() - mu N cos() ax = [N cos() - mu N cos()]/m T = -[v0x cos() m]/[N cos() - mu N cos()]...
10. ### Friction: Block on Ramp

Excellent. Thank you. For the second part, with the axes being the vertical and horizontal, I'm going to have a multi-component acceleration, yeah? In the y-direction, the forces working is the weight/gravity which is pointing in the -y-direction, and components of the Normal and Friction...
11. ### Friction: Block on Ramp

N = mg cos(theta) So, a = g sin(theta) - mu g cos(theta)? Then, v = v_0 +at Since we're looking at when it comes to rest, v=0 T = -v_0/a Look right?
12. ### Friction: Block on Ramp

I did draw a diagram. F = mu N yeah?
13. ### Friction: Block on Ramp

Homework Statement A block slides down a slope from point O with initial speed V. THe sliding coefficient, mu, brings the block to rest at time T. Using the ramp as the x-axis and the perpendicular as the y-axis, find T. Homework Equations F = ma mu = mg sin(theta) a=dv/dt The...
14. ### OPTICS - Final tomorrow - Practice test help

WVU And apparently, if you only have 3 characters in a message, it's "too short"
15. ### OPTICS - Final tomorrow - Practice test help

Homework Statement Homework Equations The Attempt at a Solution (3) I haven't been able to start this one at all. (6) I got part a (+45º P-state). I tried to do b and I got [1+i, -i+1] which isn't a polarization state, so I'm not sure what to do with c or if there is some...