Average velocity vector of non-uniform circular motion?

[Carpetfizz]

Homework Statement

A particle starting from rest revolves with uniformly increasing speed in a clockwise circle in an xy plane. The center of the circle is at the origin of an xy coordinate system. At t=0, the particle is at x=0.0m, y=2.0m. At t=2.0s, it has made one-quarter of a revolution and is at x=2.0m,y=0.0m.

(a) Speed at t=2.0s?
(b) Average velocity vector?
(c) Average acceleration vector during this interval.

Homework Equations

$$a_{tan} = \frac{dv}{dt}$$
$$a_R = \frac{v^2}{r}$$
$$a = \sqrt{a^2_{tan}+a^2_{R}}$$

The Attempt at a Solution

a)
$$r = 2$$
$$d = \frac{2 \pi (2)}{4} = \pi$$
$$v = \frac{\pi}{2}$$

b, c) I don't know where to start because it's asking for a vector which implies that we need to calculate the "average angle" ?

 

[haruspex]

Your answer for a) is wrong. what equations do you know for uniform acceleration? (Usually called the SUVAT equations.)
Also, you should state the units in the answers.