What is the correct magnitude and direction of the vector D and E?

[Frankie715]

Homework Statement

Consider the three displacement vectors

A=(3i-3j) m
B=(i-4j) m
C=(-2i+5j) m

Use the component method to determine (a) the magnitude and direction of the vector:

D= A+B+C and

(b) the magnitude and direction of:

E=-A-B+C

Homework Equations

The Attempt at a Solution

I did A+B+C which resulted in

2i-2j. I put them in the equation to find the magnitude which is

sqrt (2^2+(-2)^2) which resulted in 8. Square root of 8 is 2.82, but the back of the book says the answer is 4.47.

What am I doing wrong?

Thanks for any assistance!

 

[cupid.callin]

Well it seems good

is the answer to (b) also coming wrong?

 

[Frankie715]

Yeah,

For B) I did

arctan(-2/2) which is -45 degrees and the book says its 63.4 degrees

 

[cupid.callin]

you are doing part b wrong

its not -2/2

find E again

 

[Frankie715]

you are doing part b wrong

its not -2/2

find E again

Woops, I thought you were referring to the second part of part A to find the direction of the vector. I haven't begun part B yet. I will do it now to see if it matches the back of the book.

 

[Frankie715]

I got a magnitude of 13.4 for part B, but it is saying 8.49. What am I doing wrong?

B) -A-B+C

-6i + 12j

sqrt(36+144)=13.4

 

[Frankie715]

Anyone have any idea what I am doing wrong? I have a test on this tomorrow and would like to know how to do this (If I am doing it incorrectly).

Thanks

 

[SammyS]

Anyone have any idea what I am doing wrong? I have a test on this tomorrow and would like to know how to do this (If I am doing it incorrectly).

Thanks

Those answers seem right.

Double check the given vectors AND check that the answers are for this problem.

 

[cupid.callin]

Dont worry,
your answers are right!Sue That book's writer!