Magnitude of average velocity and derive equation

[goldenroll]

These 2 questions are confusing me, I have some idea about what to do, can someone help?

Question 1

Homework Statement

Consider a circular track with a radius of 200 meters, suppose it takes 2 minutes to run from her starting point to the opposite side of the track. What is the magnitude of her average velocity over this 2 minute interval? What is her average speed over the same interval?

The Attempt at a Solution

I did 400m/120s and got 3.33 m/s, and for speed 400m/120s = 3.33 m/s (should I be putting significant figures also or something?)


Question 2

Homework Statement

Derive Vf^2=Vi^2+2ad

Homework Equations

(I think this is equation for velocity of an object)

The Attempt at a Solution

I thought that you would treat it like a derivative and comes out to 2Vi+2, but I got it wrong.

 

[rl.bhat]

Find the length of the track along the circular path.Now find her velocity. This will be her average speed.
Initially her velocity in one direction. When she reaches the diaametrically opposite point, what is the direction of her velocity and what is the magnitude of her velocity?
Now find the average velocity.