Now
x =
2 2
t3
t 

−




Therefore
v = dx
dt  = 4t – t2 = t(4 – t)
Thus, v = 0 gives t = 0 and/or t = 4 Now v = 0 at P as well as at Q and at P, t = 0 So, at Q, t = 4 Thus, the car will
reach the point Q after 4 seconds