How can I find the velocity and acceleration of a particle in 2-dimensions?

[Filenes]

Homework Statement

The vector position of a particle varies in time according to the expression r = (7.40 i - 6.60t2 j) m.
(a) Find expressions for the velocity and acceleration as functions of time. (Use t, i, and j as necessary.)
v =
a =
(b) Determine the particle's position and velocity at t = 2.00 s.
r =
v =

Homework Equations

kinematic of 2-dimen
r= v/t

The Attempt at a Solution

I found (b) r.. but i have no clue how to start part (A), i thought since R = V/t then
r =(7.40i - 6.60t^2)/ t but that was wrong.. so I'm thinking that r should be change into something. Any help would be great

 

[LowlyPion]

What is the definition of Velocity and Acceleration with respect to distance and time?

 

[AshesToFeonix]

r/t is average velocity. your trying to find the instaneous rate of change. which means its time to put that calc 1 to use!