- #1

- 8

- 0

## Homework Statement

What is the tractive force F necessary between subway car A and the track to reach a speed of 100km/h in 1 minute? What distance was traveled during this time? At this point the brakes are fully applied on the wheels of car A in order to slow the train to 40km/h. The brakes are not applied on the wheels of car B and C. Knowing the coefficient of kinetic friction is 0.30 between the wheels and the track. Determine a) the distance required to slow the train b) time required to slow train c) force in each coupling

Ma= 25000 kg, Mb = 40000 kg, Mc = 25000 kg

## Homework Equations

m1vx1+ Fdt = m2vx2

100km/h = 27.78 m/s

## The Attempt at a Solution

Complete train

0 + F(60) = 90000(27.78)

F = 41670 N

Coupling force between A & B

0 + F(60) = 65000(27.78)

F = 30095 N

Coupling between B & C

0 + F(60) = 25000(27.78)

F = 11575 N

Question do I need to apply the frictional force over this impulse??

For distance over a minute

27.78 m/s * 60 =1668.8 m?

To find part A & B

40km/h = 11.11m/s

(Using work done)

W = Fd, work = change in PE

1/2 mv^2 = 1/2 90000(27.78 -11.11)^2 =12505000 J

d = w/f (force =ukN = 90000(9.81)0.3 = 264870

d = 12.5X10^6/264870 = 47.2 m *part A*

b) 90000 -264870(T) =90000(11.11)

t = 5.66s