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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: catdoc on July 10, 2011, 04:21:35 pm

Title: Vector subtraction help
Post by: catdoc on July 10, 2011, 04:21:35 pm: > > > >
A+B = A+(-B). Right ?

Question - carry out the following vector subtractions

A) 24 m East minus 18 m North
B) 48 m North minus 22 m South
C) 13.8 m/s East minus 9.4 m/s North

Pleas show working out or give explanation
Title: Re: Vector subtraction help
Post by: moekamo on July 10, 2011, 04:35:27 pm: A+B=A-(-B) and A-B=A+(-B)

so for a) 24m east minus 18m north = 24m east plus 18m south

b) 48m north minus 22m south = 48m north plus 22m north

c) 13.8m/s east minus 9.4 m/s north = 13.8m/s east plus 9.4 m/s south

not really sure what your meant to do with these though? are you just drawing the vectors and the resultant vector?
Title: Re: Vector subtraction help
Post by: catdoc on July 10, 2011, 05:01:32 pm: This question is from Nelson physics 12 pg.7 the question is written as above the answers are

a) 6 m North
b) 70 m North
c) 16.7 m s–1 S56°E

i dont understand how to work them out.

link to question, page 7 question 3

http://www.mediafire.com/?unwrm1dnzdz

link to answers, chapter 1, set 1A question 3

http://www.mediafire.com/?2nmnzyjt2zw
Title: Re: Vector subtraction help
Post by: moekamo on July 10, 2011, 05:14:27 pm: are you sure a) isnt: 24 m North minus 18 m North, that would work out as 6m North.

b) well i just didnt simplify it in the last step, 48m north + 22m north= 70m north

c) draw a diagram and use pythagoras to get the hypotenuse of the triangle( $h=\sqrt{13.8^2+9.4^2}=16.7$ )
then to get the direction, use trig to get the angle as $\theta = \arctan \frac{9.4}{13.8}=34.26^\circ$ then the angle relative to south is 90 - theta = 55.74 degrees
Title: Re: Vector subtraction help
Post by: catdoc on July 10, 2011, 05:28:45 pm: yes sorry it was 24 m north minus 18 m north