physics
posted by PLZ HELP ME NOW... .
a train starts from rest and accelerates uniformly at 100m/min^2 for 10 min.then it maintains a constant velocity for remaining 20 min.brakes are applied and train uniformly retards and comes to rest in next 5 min.
a)the maximum velocity reached
b)the retardation in last 5 min
c)total distance traveled
d)the average velocity of the train.

v=a•t1 =100•10 = 1000 m/min.
s1 = a1•t1²/2 =100•100/2 =5000 m.
s2=v•t2 =1000•20 =20000 m.
0 =v +a2•t3,
a2 = v/t3 =  1000/5 =  200 m/min,
s3 = v •t3 – a2•t3²/2 =1000•5  200•25/2 =2500 m
s = s1 + s2 +s3 = 5000 + 20000+ 2500 = 27500 m.
t =t1+t2+t3 = 10 +20 =5 = 35 min.
v(ave) =s/t = 27500/35 =785 m/min.
a) 1000 m/min,
b)  200 m/min,
c) s = 27500 m.
d) v(ave) =785 m/min.