# Work done by cables on railroad cars

1. Oct 25, 2009

### acherentia

1. The problem statement, all variables and given/known data
Two railroad cars, each of mass 1.6 104 kg, are connected by a cable to each other, and the car in front is connected by a cable to the engine as shown in the figure below. The cars start from rest and accelerate to a speed of 1.9 m/s after 1 min.

(a) Find the work done by cable 1 on the car in the back.

(b) Find the work done by cable 1 on the car in front.

(c) Find the work done by cable 2 on the car in front.

http://s966.photobucket.com/albums/ae146/acherentia/?action=view&current=6-p-011.gif

2. Relevant equations

W=F*d

W=delta KE

KE=1/2 m v^2

3. The attempt at a solution

FOR A I need to find the speed at which the cable 1 pulls on the car in the back. How?

B asks for the work cable 1 does on the car in front and it will be the result for A with "-" in front

FOR C I should know the work done on the car in front, which is actually the work done on the car in front, car in the back and cable between them. How do I express this?

Thank you!

2. Oct 25, 2009

### Delphi51

The speeds of the cars, cables and engine are all the same.
Perhaps you could use E1 for the energy of the car in the back and E2 for the energy of the front car. What formula will you use to calculate E1?

3. Oct 25, 2009

### acherentia

Hi,

i just realized the problem is really simple. a delta x= (vf^2-vi^2)/2 and that is enough to find work for a), b) is the negative result of a and c) is twice the result of a.