## baddinlol 3 years ago An object is moving with constant speed in a straight line relative to O. the objects initial and final position vectors are respectively: u = i + 2j + 3k, v = 2i + j -4k, Find expression for q the position vector of the object when it has travelled a distance of x.

Ok, so I am having a bit of trouble with this one.

2. shana91

is the diagram clear? |dw:1331119632568:dw|

3. shana91

do you knwo how to take vector UV?

Yes -u + v

5. shana91

|dw:1331119715424:dw|

Yep.

I was thinking maybe q = (v-u) + xu

8. shana91

ok so it gives, UV as i-j-7k. when it is at distance 0, the vector is U, when it is in its end, the vector is V so when it has travelled X it should be in between right? so the answer when it is after x distance is, |dw:1331119912201:dw|

9. shana91

when it is at x distance, it is the UNIT VECTOR*X i have found the unit vector by dividing by the scalar value of the vetor which is $\sqrt{1^2+1^2+7^2}$

Why are we using the unit vector though?

11. shana91

Unit vector means= what's the direction and the magnitude a particle will have when x=1(it has gone by one UNIT) so to get x units you have to multiply by X

Oh.. ok That makes it clear.. Thanks for your help.

13. shana91

welcome :)