How Do You Calculate Acceleration and Retardation for a Train's Movement?

[scotthands]

Homework Statement

A train accelirates uniformly from rest to reach a speed of 54km/hr in 200 seconds after which the speed remains constant for 300 seconds, At the end of this time the train decelerates to rest in 150 seconds.

Calculate the acceleration and retardation.

Homework Equations

s= ut
v= u+at
s=ut + 0.5*at^2

The Attempt at a Solution

a = (v-u)/t = 54/(200/60*60)=972km/h^2

is the first part correct? I'm not really sure what to do next.

 

[Sourabh N]

First part is correct; in second part speed is constant, hence no acceleration and third part is similar to first part.

 

[ogb p]

Yes, your calculation for acceleration is correct. To calculate the retardation, we can use the same equation:

a = (v-u)/t

Where:
v = final speed (0 km/hr)
u = initial speed (54 km/hr)
t = time (150 seconds)

a = (0-54)/150 = -0.36 km/h^2

Therefore, the acceleration is 972 km/h^2 and the retardation is -0.36 km/h^2. This means that the train is accelerating at a faster rate than it is decelerating.