The acceleration of a particle moving only on a horizontal plane is given by a= 3ti 4tj, where a is in meters per second-squared and t is in seconds.

At t = 0s, the position vector r= (20.0 m)i (40.0 m)j locates the particle, which then has the velocity vector v= (5.000 m/s)i (2.00 m/s)j

(a) What is the expression of its instantaneous velocity vector, as a function of time?
(b) What is the expression of its instantaneous position vector, as a function of time?

At t = 4s, what are :

(c) its position vector in unit-vector notation?
(d) the angle between its direction of travel and the positive direction of the x axis