Question

A body starts from rest and moves with uniform acceleratio. Of 5m/s2 for 8s from that time the acceleration ceases find the distance covered in 12s starting from rest

Answer 1

after 8s the final velocity is v= u+ at = 0 + 5 * 8 = 40 m/s
distance covered in 8s is s= ut + 0.5*at^2 = 0 + 0.5*5*64 = 160 m
now for the next 4 seconds the acceleration is zero so 40 m/s is maintained 
so distance covered in 4 sec = ut = 40 * 4 = 160 m

thus distance in 12 s = 320 m