Hey can you guys give me some help with this physics problem.. having real issues figuring it out, and ive looked all over the internet. Google'd like 100 times...

A Particle at Constant Speed A particle P travels with constant speed on a circle of radius r = 3.35 m (Figure 5-39) and completes one revolution in 20.0 s. The particle passes through O at time t = 0. State the following vectors in magnitude-angle notation (angle relative to the positive direction of x).

The picture of it...
http://www.webassign.net/hrw/166710.gif

1.) With respect to O, find the particle's position vector at the time t = 5.00 s.

I figured out the angle, but i cant figure out how to get the position vector. Just so u know, in case u try the problem, ive already tried the following answers, that are apparently wrong : 1.05, 4.21, .948, 5.26, and 3.35

the rest of the questions are similar to #1, so if u guys can help me with that one, i can figure out the rest.

Thanks
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 Have you drawn the picture where t=5s? In case you are looking for the magnitude of vector OP at that time, pythagoras should do it, right?
 i did draw a picture, that really didnt do much though. I got that part of the question actually, apparently i was supposed to use the equation a (position vector0 = SqRt(ax^2+ay^2). And since it went 3.35 in the x direction, and 3.35 in the y direction, at time=5s, i got an answer of 4.74 However, I cant figure it out for when t=7.5seconds I figured out that the angle is 67.5, and that is correct... but i cant get the position vector. I apparently need to use the formula that i used for the 1st one, but the answers i tried didnt work, can anyone help with that?