# Homework Help: Newton's Second law problem; rail and cart model.

1. Dec 6, 2007

### kplooksafterme

1. The problem statement, all variables and given/known data
A 800 g steel "cart" has a square steel rail running through the middle of it, touching the steel cart on all four sides of the rail. An elastic cord attached to the front of the cart and the "ceiling" of the apparatus creates a 45 degree angle from the horizontal axis in front of the cart to the cord. Given that the tension in the cord is 20N and the coeeficient of kinetic friction is 0.6, what is the initial acceleration of the cart? (The cart is released when the angle between the horizontal axis and the cord is 45 degrees.

2. Relevant equations
$$\sum$$ FnetX = Tcos45 - fk = ma
$$\sum$$ FnetY = Tsin45 + N(rail on top part of cart) - w - N(rail on bottom part of cart) = 0
Also, the two normal forces of the rail on the cart pushing out on the sides of the cart are N(rail on left side of cart) - N(rail on right side of cart) = 0

3. The attempt at a solution
I don't have a clue how to solve for these normal forces, any ideas?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution