Thursday
May 5, 2016

Homework Help: physics multiplying vectors

Posted by sam on Thursday, March 29, 2007 at 9:43pm.

n the product F = qv · B , take q = 4,
= 2.0i + 4.0j + 6.0k and = 136i -176j + 72k.
What then is in unit-vector notation if Bx = By?

~~may i get some assistance in this problem? so far.. i tried this..

136i-176j+72k = 4(2.0i+4.0j+6.0k)(B)
136i-176j+72k = (8i+16j+24k)(B)
[(136i-176j+72k)/(8i+16j+24k)] = B
17i-11j+3k = B

thats wrong.. so should i be doing this?
136i-176j+72k = (8xi+16yj+24zk)(Bxi+Byj+Bzk)
136i-176j+72k = (8xBxi+16yByj+24zBzk)
???

i need some help asap, that would be great. thanks again!

* physics multiplying vectors - drwls, Thursday, March 29, 2007 at 4:37pm

Fill in the blanks in your question
<< In the product F = qv · B , take q = 4,
___= 2.0i + 4.0j + 6.0k and ___= 136i -176j + 72k.
What then is ___ in unit-vector notation if Bx = By>>
If the B vector is 2.0i + 4.0j + 6.0k, then Bx and By are NOT equal. Your question is incomplete and does not make sense.

* physics multiplying vectors - bobpursley, Thursday, March 29, 2007 at 4:38pm

You didn't multiply...

136i-176j+72k = (8i+16j+24k)(B)
But B= Bxi +Byj + Bzk
136i-176j+72k = (8i+16j+24k)(Bxi +Byj + Bzk)
136i-176j+72k= 8Bx k -8By j + 16Bx k +16Bz i + 24Bx j- 24By i

Now gather the terms, set the i terms equal to i, and so on. Check my work, I did it in my head.

* physics multiplying vectors - sam, Thursday, March 29, 2007 at 9:37pm

sorry, the complete question is:

n the product F = qv · B , take q = 4,
v = 2.0i + 4.0j + 6.0k and F= 136i -176j + 72k.
What then is in unit-vector notation if Bx = By?

I still can't get the right answer though...

Bobpursley...at this step:
136i-176j+72k = (8i+16j+24k)x(Bxi+Byj+bzk) I didn't think that you could just multiply the two vectors on the right hand side since they are both vectors not scalars. I have 3 vectors and I am trying to solve for B. How do I do that after this step?

thanks, i figured it out.