• Support PF! Buy your school textbooks, materials and every day products Here!

Proton moving through magnetic field

  • #1

Homework Statement



A proton moves through a uniform magnetic field given by =(6.97-9.54+35.0) mT. At time t1, the proton has a velocity given by =vx+vy+(1.58 km/s) and the magnetic force on the proton is FB=(4.72 X 10-17N)+(3.45 X 10-17N).

(a) At that instant, what is vx?

(b) At that instant, what is vy?

Homework Equations


F=qV x B

The Attempt at a Solution



So, in order to find the velocity in the x direction I am assuming you do this:
(4.27E-17)i +(3.45E-17)j=e[(vx+vy+1.58k)x(6.97i-9.54j+35k)]

That is really all I have because I cant figure out the cross product. I end up with vx terms in the j direction and I don't know what to do with them. I hope I am making sense. Please let me know if youcan help. THANK YOU!!!
 

Answers and Replies

  • #2
berkeman
Mentor
56,616
6,519
Could you please clarify your vector velocity and B-field components? And then show how you derived the vector force components? Please label the x, y, and z components explicitly in each equation.
 
  • #3
they are given in the problem

b= (6.97i-9.54j+35.0k)

and the vector force was not derives as is also given in the equation as: (vx)i+(vy)j+(1.58 km/s)k
 
  • #4
berkeman
Mentor
56,616
6,519
You have the field and the charge and the initial veloity. You have what you need. What are the relevant equations?
 
  • #5
674
2
You did leave off the i, j, and k unit vectors when describing the problem which left a little to the imagination. But it looks like your equation:

(4.27E-17)i +(3.45E-17)j=e[(vx+vy+1.58k)x(6.97i-9.54j+35k)]
looks correct so far. Could you show us the cross product you ended up getting so we could see if you did something wrong? And getting a vx term in the j direction is alright. Once you have the cross product, you just equate the i-terms on both sides of the equation, and do the same for the j- and k-terms and solve.
 
  • #6
for the cross product i got:
(35vy+15.07)i+(35vx-11.07)j+(-9.54vx-6.97vy)k

if I do this:
(4.72E-17)=(35vy+15.07) and I solve for vy that is what the velocity in the x directions is? .431? Why am I solving for vy if i am looking for vx?
 
  • #7
hmm I bet I need to convert the mT to T huh?
 

Related Threads for: Proton moving through magnetic field

Replies
6
Views
5K
Replies
2
Views
2K
  • Last Post
Replies
4
Views
5K
  • Last Post
Replies
10
Views
11K
Replies
4
Views
18K
Replies
7
Views
10K
  • Last Post
Replies
1
Views
2K
Top