Question

A motor car starts from rest and accelerates uniformly for 10s to a velocity of 20m/s. it then runs at a constant speed and is finally brought to rest in 40m with a constant acceleration. total distance covered is 640m. find the value of accelartion retardation and total time taken.

Answer 1

GIVEN:

1.Uniform acceleration for 10s to a velocity of 20 m/s.
2.Constant speed at 20 m/s.
3.bought to rest in 40 m.
4.Total distance covered 640 m.

TO FIND: 

1.Acceleration.
2.Retardation.
3.Total time taken.

SOLUTION
   We know that a = (v - u) / t .Then,
a = (20 - 0) / 10 
a = 20 /10
==> a = 2 m / s*s 
   We also know that retardation = (v - u) / t.Then,
r = (0 - 20) / 10
r = 20 /10
==> r = -2 m / s*s
    We also know that v = u + at
0 = 40 + -2*t 
-40 = -2*t
40/2 = t
 ==>  20s = t