a. How much time elapses from start to stop
v = u + at
20 = 0 + 2t1
t1 = 10 sec
2nd phase:
v = u - at
0 = 20 - 1 x t2
t2 = 20 sec
total time = t1+t2 = 10 + 20 = 30 sec
b.1st phase:
s = ut + 1/2at^2
s1 = 0 + 1/2 x 2 x (10)^2
s1 = 100 m
2nd phase:
By s = ut - 1/2at^2
s2 = 20 x (20) - 1/2 x 1 x (20)^2
s2 = 200 m
total distance(s) = s1+s2 = 100 + 200 = 300 m
hope this helps
