Re: [NSW] Cityrail Grades

["Gnome 412" <gnome412@hotmail.com>]

Jonathan Boles wrote in message ...
>Year 9 maths (!):  m is standard pronumeral for gradient
>m = (y1 - y2) / (x1 - x2) , where x1,y1 and x2,y2 are two points.
>
>Here,  m = dy/dx, therefore y = distance of (y1 - y2), which is directly
>proportionate to x, but only if m is fixed, as is the case at a single
point
>of railway track.


So, in amongst all the posters who have'nt a clue, we have somebody who
could answer this hypothetical probem (which is on topic because it involves
a CityRail grade):

A train is travelling at 42 km/h on a falling grade of 1 in 60.
The driver notices an obstacle 100m ahead and applies full emergency brakes
or drops the dead-man handle.
Assume that the driver's reaction time is 1 second and the brakes take 4 sec
to suddenly apply.
Assume that the braking force is limited by a coefficient of friction
between the brake shoes / wheels (and between the wheels / rails) of 0.20.
Assume g = 9.8 m/s/s

At what speed is the train travelling after it has travelled 100m?

Hint:  the accelleration after the brakes apply will be -0.20*g + g/60

This seems to have stumped a room full of QCs for two months.

Rgds