Physics- Elena please help!

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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! -

    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! -

    Can you tell me the values you are getting so I can make sure I did the algebra right?

  • Physics- Elena please help! -

    How about the other way around? You post the values and I check. I already took the course (in 1955).

  • Physics- Elena please help! -

    For Tension I am getting 117.4

  • Physics- Elena please help! -

    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! -

    What is the label for the work? I tried Newtons and that is wrong.

  • Physics- Elena please help! -

    Work is in Joules !!!!

  • Physics- Elena please help! -

    work done against friction = ENERGY lost
    That is JOULES !

  • Physics- Elena please help! -

    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! -

    We did part C immediately

    T cos 40 = 63.2 = pull force = friction force

  • Physics- Elena please help! -

    It is not accelerating so friction force is equal and opposite to pulling force.

  • Physics- Elena please help! -

    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.

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