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October 14

direction relative velocity

In an inertial coordinate system, a particle's position as a function of time is given by r=i(1 m/s^3)t^3 -j(2m/s^2)t^2 & a student's position by r=-j(2m/s^2)t^2 +k(3m/s)t, for the interval 0 to 2s

I'm asked to compute the direction of a particle's average velocity relative to the student for this 2 second interval (I know I need either two angles, or a plane and one angle)

I've calculated that the relative average velocity of the particle to the student is -4i m/s +3k m/s

How do I find the direction from that?24.63.107.0 (talk) 05:43, 14 October 2010 (UTC)[reply]

The direction of the vector −4i m/s +3k m/s is the unit vector −0.8i+0.6k. Bo Jacoby (talk) 07:11, 14 October 2010 (UTC).[reply]

Or if you need the direction as an angle, you can convert it to polar coordinates ( arctan(3/4) ). --131.188.3.21 (talk) 07:57, 14 October 2010 (UTC)[reply]

I think you have your signs reversed - to calculate the velocity of the particle relative to the student, you should subtract the student's velocity from the particle's velocity, not vice versa. Gandalf61 (talk) 08:59, 14 October 2010 (UTC)[reply]