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**djmccabie** A particle P moves such that its position vector **r** with respect to the origin O at the time *t *is given by

**r = **cos3*t***i** + sin3*t***j**

a) Find an expression for **v, **the velocity of P at time *t.*

b) Show that the direction of **v** is perpendicular to that of **r **for all values of *t.*

c) Find the speed of P.

OK for part a I'm assuming you differentiate **r** which i get

**v** = -3sin3t**i **+ 3cos3t**j**

is this correct??Part b Im stumped with, not sure I've learned that.

For part c i think maybe i use equation v=u+at ??

if so how could i find t ?