# Vector problem.

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#1
Hi, need help with this question.

'Two forces acting on a rocket are represented by vectors u and v.
-----( 2)-----------( 7 )
u = (-5) and v = ( 4 )
-----(-3)-----------(-1 )

(^sorry, I didn't know how to display vectors! )

Calculate |u+v|, the magnitude of the resultant force.

I am able to work out the resultant vector but then have no idea how to put that into a surd! Add i can't find how to anywhere on the internet!

0
7 years ago
#2
(Original post by jam321)
Hi, need help with this question.

'Two forces acting on a rocket are represented by vectors u and v.
-----( 2)-----------( 7 )
u = (-5) and v = ( 4 )
-----(-3)-----------(-1 )

(^sorry, I didn't know how to display vectors! )

Calculate |u+v|, the magnitude of the resultant force.

I am able to work out the resultant vector but then have no idea how to put that into a surd! Add i can't find how to anywhere on the internet!

Do you know how to find the magnitude? If so just leave in the form .
0
#3
(Original post by BabyMaths)
Do you know how to find the magnitude? If so just leave in the form .
No, I don't know how to find the magnitude.
0
7 years ago
#4
Generally speaking, for a 3 dimensional vector of the form (x, y, z), its magnitude is simply (x^2 + y^2 +z^2 ) ^(1/2) .

Hope this helps. Peace.
0
#5
Thanks that helps but the answer is 7(sqrt2) and I don't know how to get there. Do you first add the vectors together, then find the magnitude as how you said and then just leave it in surd form?
If that is how you do it, I'm not getting 7(sqrt2).
0
7 years ago
#6
(Original post by jam321)
Thanks that helps but the answer is 7(sqrt2) and I don't know how to get there. Do you first add the vectors together, then find the magnitude as how you said and then just leave it in surd form?
If that is how you do it, I'm not getting 7(sqrt2).
What did you get for u+v?
0
7 years ago
#7
(Original post by jam321)
TDo you first add the vectors together, then find the magnitude as how you said and then just leave it in surd form?
Yes. do that.
If that is how you do it, I'm not getting 7(sqrt2).
Then your calculation is not right.
e.g. do you have (-1)+(-3)=(-4) ?
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#8
The resultant vector I have is: x=(9), y=(-1) and z=(-4) which I'm pretty sure is right.

I think then it must be the way I am working out the magnitude...
0
7 years ago
#9
(Original post by jam321)
The resultant vector I have is: x=(9), y=(-1) and z=(-4) which I'm pretty sure is right.

I think then it must be the way I am working out the magnitude...
One common mistake is to do -4^2 on the calculator and not realise that this gives you -16.

You need (-4)^2 or just write 16 straight away.
0
7 years ago
#10
(Original post by jam321)
Hi, need help with this question.

'Two forces acting on a rocket are represented by vectors u and v.
-----( 2)-----------( 7 )
u = (-5) and v = ( 4 )
-----(-3)-----------(-1 )

(^sorry, I didn't know how to display vectors! )

Calculate |u+v|, the magnitude of the resultant force.

I am able to work out the resultant vector but then have no idea how to put that into a surd! Add i can't find how to anywhere on the internet!

One word: Pythagoras
0
7 years ago
#11
(Original post by StarvingAutist)
One word: Pythagoras
two words: Pythagoras' Theorem
0
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