Yet another M1 question....~_~

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Hey guys

Could someone please help me on this question i've totally lost all understanding of vectors lol

A particle P is moving with a constant velocity (3i+2j)m-1. At time t=6s, P is at the point with position vector (-4i-7j)m. Find the distance of P from the origin at time t=2s.

thanks

Posted: 09-05-11 09:40 by Stacy

I'm confused, maybe look at mymaths... it might help

Posted: 14-05-11 15:13 by Emma

I think I've solved it but you will have to check

First I used the equation r = ro + vt (position vector = original position + (velocity x time)to find the original position

so -4i - 7j = ro + 6(3i + 2j)

-4i - 7j = ro + 18i + 12j

ro = -22i - 19j

Then i used the same equation to find the position at t=2

r = -22i - 19j + 2(3i + 2j)

r = -22i - 19j + 6i + 4j

r = -16i -15j

This is the distance from the origin in vectors so I used pythagoras to find the actual distance from the origin

a2 + b2 = c2

(-16)2 + (-15)2 = c2

c2 = 481

c = 21.9317122

distance from the origin at t=2 is 22m (2 significant figures)

Hope that helps :-)

Are you doing edexcel? x

Posted: 15-05-11 17:31 by AnnaLouise

wow! Long workings man!! lol Well done!! :D

Posted: 15-05-11 17:39 by Emma

Is it right? x

Posted: 15-05-11 19:18 by AnnaLouise

yupo doing edexcel......................(checks question)....... ans is 17m http://www.kingsleyschoolbideford.co.uk/Images-(1)/SeniorSchool/Maths-PDFS/M1_MS_20100608.aspx 

teacher told me it was position vector at 6s + velocity(-4) <- -4 comes from 6-2 

But Thanks a lot anyway i really couldn't get my head around the question I despise vectors!!

Posted: 15-05-11 20:46 by Stacy

actually seeing as we are the topic of Mechanics does anyone know how to decide which way the resolving forces go when u are working it out? it drives me insane i always get my signs the wrong way! anyone?.....

Posted: 15-05-11 20:49 by Stacy

I know I hate vectors too!

Posted: 16-05-11 11:59 by AnnaLouise