Homework Help: Vector addition and magnitude

1. Sep 16, 2007

B-80

If B is added to C = 2.5 i + 3.5 j, the result is a vector in the positive direction of the y axis, with a magnitude equal to that of C. What is the magnitude of B?

I have tried 0, which seems to make sense to me, but it is wrong. and I don't know if it means b+c=2.5i+3.5j or if b=? and c=2.5i+3.5j. Also how can a resultant vector = one of its components if the other vector has any value?

2. Sep 16, 2007

learningphysics

"the result is a vector in the positive direction of the y axis with a magnitude equal to that of C"

first calculate this vector.

3. Sep 16, 2007

B-80

okay, 4.3

4. Sep 16, 2007

learningphysics

yes, that's the magnitude... what's the vector?

5. Sep 16, 2007

B-80

idk I don't have the angle? unless the first vector they gave was the resultant? is that how it sounds to you?

6. Sep 16, 2007

tabchouri

you have the magnitude of B+C wich is 4.3, you know also that B+C is in the positive direction of y
so
B + C = 4.3 j
let B = a i + b j
so
B + C = (a i + b j) + (2.5 i + 3.5 j ) = 4.3 j

the rest : what are a & b that define B ?

7. Sep 16, 2007

B-80

-2.5 + .7, so 2.6, thanks

8. Sep 16, 2007

B-80

I am also having trouble with
Here are three vectors in meters: d1 = -3.0 i + 3.0 j + 2.0 k, d2 = 2.0 i + 3.0 j + 2.0 k, d3 = -2.0 i - 6.0 j + 1.0 k. What results from the following products?

(a) d1· (d2 + d3)

(b) d1· (d2 d3)

(c) d1 (d2 + d3)

9. Sep 16, 2007

dynamicsolo

The first is going to involve a dot product calculation, but there is something odd about your statement of parts (b) and (c). How is part (c) different from (a)? Please check how the rest of the problem is notated -- that is very important!

10. Sep 16, 2007

B-80

cool, got that one, but have another one:

In the product = q , take q = 3,

= 2.0i + 4.0j + 6.0k and = 138i -168j + 66k.

What then is in unit-vector notation if Bx = By?

11. Sep 16, 2007

dynamicsolo

What is being multiplied in the product? Some number of labels in this problem aren't showing up. I wonder if you've used some feature the forum software doesn't like or whether my browser doesn't read it?

12. Sep 16, 2007

B-80

In the product F = qV + B , take q = 3,
V= 2.0i + 4.0j + 6.0k and F= 138i -168j + 66k.
What then is in unit-vector notation if Bx = By?
sorry about that

13. Sep 16, 2007

B-80

hey this is due at 11:45 est, so any help is really appriciated

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook