- #1
dorkymichelle
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Homework Statement
Figure 7-40 shows a cord attached to a cart that can slide along a frictionless horizontal rail aligned along an x axis. The left end of the cord is pulled over a pulley, of negligible mass and friction and at cord height h = 1.2 m, so the cart slides from x1 = 3.0 m to x2 = 2.0 m. During the move, the tension in the cord is a constant 27.0 N. What is the change in the kinetic energy of the cart during the move?
Homework Equations
W= Fdcos a
W = 1/2mvf2 - 1/2mvi2
w = change in kinetic energy
The Attempt at a Solution
I think I can just find work because change in kinetic energy(what the prob. asks for) = net work
Only the component of force that is parallel to the displacement is doing work.
Using the triangle between displacement and the cord, I get a = 50.19 degrees
x component of force = cos 50.19=x/27.0, Fx = 17.28
W = f*d
W = 17.28 *1.0m
since x1= 3.0m and x2 = 2.0m, displacement is 1.0m
so W = 17.3 J
change in kinetic energy = 17.3 J
what did i do wrong?