4. the vector position of a particle varies in time according to the expression f = 8.00i - 6.80t^2; where r is in meters and t is in seconds (a) Find an expression for the velocity of the particle as a function of time. (Use any variable or symbol stated above as necessary.) V= m/s (b) Determine the acceleration of the particle as a function of time. (Use any variable or symbol stated above as necessary.) m/s2 a= (c) Calculate the particle's position and velocity at t = 3.00 s r= v=