2005 Module 2 Layout Calculations

[dorothy.pipet]

Hi,

In sheet 4 of DAP calculations, extra time is calculated by half of the accelerating/decelerating time.

can someone please let me know the reason for considering half of the time.

Thanks in advance.

Here we are comparing two times to cover the same distance:
(1) at constant speed
(2a) while accelerating from rest
(2b) while declerating to rest.
Since the accerleration rate and braking rate are identical, 2a=2b.

now if a train is proceding at constant speed the time is t1=distance/speed

But if it is constant acceleration we would use the AVERAGE speed, t2=distance/average speed.
The average speed (v-u)/2 in this case is half the (initial) speed.

It follows that t1=0.5 t2