Posted by Anonymous on .
A sled loaded with bricks has a total mass of 18.0 kg and is pulled at constant speed by a rope inclined at 40.0o above the horizontal. The sledge moves a distance of 16.0 m on a horizontal surface. The coefficient of kinetic friction between the sledge and surface is 0.510 .
(a) What is the tension in the rope?
b) How much work is done by the rope on the sled?
c)What is the magnitude of the force of friction?
(d) What is the mechanical energy lost due to friction?

Physics Elena please help! 
Damon,
force pulling sled = T cos 40
force lifting sled = T sin 30
normal force = mg  T sin 40
friction force = 0.51(mg  T sin 40)
acceleration = 0
so
friction force = pulling force
so
0.51(mg  T sin 40) = T cos 40
solve for T
then work = 16 * T cos 40
etc 
Physics Elena please help! 
Anonymous,
Can you tell me the values you are getting so I can make sure I did the algebra right?

Physics Elena please help! 
Damon,
How about the other way around? You post the values and I check. I already took the course (in 1955).

Physics Elena please help! 
Anonymous,
For Tension I am getting 117.4

Physics Elena please help! 
Damon,
m g = 177 N
.51 (177  .643 T) = .766 T
90.3  .328 T = .766 T
T = 82.5 N
T cos 40 = 63.2 = pull force = friction force
63.2 * 16 = 1012 Joules = work done (also energy lost to friction) 
Physics Elena please help! 
Anonymous,
What is the label for the work? I tried Newtons and that is wrong.

Physics Elena please help! 
Damon,
Work is in Joules !!!!

Physics Elena please help! 
Damon,
work done against friction = ENERGY lost
That is JOULES ! 
Physics Elena please help! 
Anonymous,
Oh ya, I understand part a and b now, but I am still confused on part c. How would I solve this?

Physics Elena please help! 
Damon,
We did part C immediately
T cos 40 = 63.2 = pull force = friction force 
Physics Elena please help! 
Damon,
It is not accelerating so friction force is equal and opposite to pulling force.

Physics Elena please help! 
Damon,
Now slow down and draw a good picture and follow what I did carefully step by step. I have to go coach a high school sailing team now.