Vector problem.

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.
Express your answer as a surd in its simplest form'

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!

Thanks in advance.

Reply 1

BabyMaths

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.
Express your answer as a surd in its simplest form'

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!

Thanks in advance.

Do you know how to find the magnitude? If so just leave in the form

a \sqrt{b}

.

Reply 2

jam321

OP

Original post by BabyMaths

Do you know how to find the magnitude? If so just leave in the form

a \sqrt{b}

.

No, I don't know how to find the magnitude.

Reply 3

WhiteGroupMaths

9

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.

Reply 4

jam321

OP

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).

Reply 5

BabyMaths

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?

Reply 6

ztibor

10

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) ?

Reply 7

jam321

OP

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...

Reply 8

BabyMaths

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.

Reply 9

StarvingAutist

17

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.
Express your answer as a surd in its simplest form'

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!

Thanks in advance.

One word: Pythagoras

Reply 10