The displacement in feet of a certain particle moving in a straight line is given by 8 t3 6 where t is measured in seconds a Find the average velocity over the given time periods 1 1 3 2 1 2 3 1 1 5 4 1 1 1 b Find the instantaneous velocity at t 1 1 2 3 4 b ft s ft s ft s ft s ft s