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Crate pulled up incline, kinetic energy and speed; picture included

  1. Oct 4, 2010 #1
    1. The problem statement, all variables and given/known data
    A crate is pulled by a force (parallel to the incline) up a rough incline. The crate has an initial speed shown in the figure below. The crate is pulled a distance of 5.94 m on the incline by a 150 N force.
    The acceleration of gravity is 9.8 m/s2 .
    [​IMG]
    a) What is the change in kinetic energy of the crate?
    Answer in units of J.
    b) What is the speed of the crate after it is pulled the 5.94 m?
    Answer in units of m/s.

    2. Relevant equations
    (1)W= delta K= Integral Fx dx= Integral Sum of F dr= Integral Sum of F dr + Integral fk dr= Sum of W - fkd
    (2)Delta K= 1/2 mvf^2

    3. The attempt at a solution
    Wells for part a) I tried equation (1)and got 150 N- (0.399* 5.94)=147.63 J... which I don't know if its right
    and for b) (if part a is right) I used equation (2) vf=sq rt ( (2/m)*147.63)= 4.76574 m/s
     
  2. jcsd
  3. Oct 4, 2010 #2

    PhanthomJay

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    When using W =delta K , W includes the work done by gravity or any other conservative forces, when present. It is best to use conservation of total energy, Work done by non - conservative forces (like friction and the applied force) equals delta __??__ + delta __??_.

    The problem asks for the change in Kinetic Energy, in addition to its speed.

    You are getting your energy and force units mixed up.
     
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