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Homework Statement
A farmer hitches her tractor to a sled loaded with firewood and pulls it a distance of 20m along level ground. The total weight of sled and load is 14700N. The tractor exerts a constant 5000N at an angle of 36.9 above the horizontal. There is a 3500N friction force opposing the sled's motion. Find the work done by each force acting on the sled and the total work done by all the forces.
The Attempt at a Solution
To start off,
I found the work done by each force.
I drew the figure as follows:
http://img254.imageshack.us/img254/3663/49497726xp3.jpg
my calculations
cos(angle) = x/5000
5000 cos 36.9 = 3998.42
(3998.42J)(20m) = 79968.47
and
3500cos180 = -3500
(-3500J) (20m) = -70000
79968.47-70000 = 9968.47
My answer: 9968.47
Book answer: 10000
Is my process wrong, if so where did I go wrong? Don't the gravity and normal force cancel out?
From my reading in the book, we suppose to only count the horizontal forces, which is what I did here.
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