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# M1 velocity stuff (Help!) watch

1. It says the motion of a particle (position vector) r(t) is:

r(t) = 2cos(6t)i+2sin(4t)j

1. It asks me to describe the motion in my own words, so what do I actually have to say?

Is it going 2cos(6t) in the i and 2sin(4t) in the j direction?

2. How are the acceleration and r(t) = 2cos(6t)i+2sin(4t)j related?
Do i just say you differentiate r(t) twice to get the acceleration?
2. (Original post by rpan161)
It says the motion of a particle (position vector) r(t) is:

r(t) = 2cos(6t)i+2sin(4t)j

1. It asks me to describe the motion in my own words, so what do I actually have to say?

Is it going 2cos(6t) in the i and 2sin(4t) in the j direction?

2. How are the acceleration and r(t) = 2cos(6t)i+2sin(4t)j related?
Do i just say you differentiate r(t) twice to get the acceleration?
If my memory doesn't fail me that would be some kind of circular/elliptical graph if you plotted it on axis.

As for the second bit, I think so, at least that's what I'd do (maybe stand back for a bit after you've differentiated twice just to see if there are any obvious comments you can make on it).
3. Thanks, how would i plot it? like t=0, 1, 2 etc..?
4. (Original post by rpan161)
Thanks, how would i plot it? like t=0, 1, 2 etc..?
I'm sure there's a more efficient way but I can't really remember it at the moment, so try plotting it as you said, just set t=0, 1, 2, 3, ...
5. hmm okay thanks, i'll see how it goes
6. If you're going to plot the function, I'd be inclined to use multiples and fractions of pi as the values for t.

Note: This won't be a trivial circle or ellipse. In fact I'm slightly surprised it's M1, given the difficulty of most of the other M1 questions I've seen on here.

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Updated: February 10, 2010
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