If a ball is thrown into the air with a velocity of 40 ft/s, its height in feet after t seconds is given by y=40t−16t2.

a. Find the average velocity for the time period beginning when t=2 and lasting

(i) 0.5 second,

(ii) 0.1 second,

(iii) 0.05 second,

(iv) 0.01 second.

b. Find the instantaneous velocity when t=2.