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How to calculate the change in kinetic energy on a plane?

  1. Feb 28, 2015 #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 9.33 m on the incline by a 150 N force. The acceleration of gravity is 9.8 m/s 2 . What is the change in kinetic energy of the crate? Answer in units of J.
    Mass = 11kg
    Angle of the incline (θ)= 20°
    Initial Velocity = 1.55 m/s
    μ = .308
    D= 9.33 Meters
    Force Applied = 150N
    g=9.8

    2. Relevant equations
    Ff= μN
    W=Fd=ΔKE
    Fapplied -Ff=Fnetx
    FnetVertical =0


    3. The attempt at a solution
    N-mgcosθ=0
    N=mgcosθ
    Fa-Ff=Fnet
    Fa-μN
    Fa-μmgcosθ=Fnet
    150-(.308)(11)(9.8)cos(20°)=118.8
    W=ΔKE = 118.8(9.33) = 1399.5

    Not sure what I am missing but it is incorrect.
     
  2. jcsd
  3. Feb 28, 2015 #2

    Nathanael

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    Homework Helper

    You've forgotten the other (parallel-to-the-plane) component of gravity.
     
  4. Feb 28, 2015 #3
    My force should look like this then?

    force applied - force friction - mgsinθ= Fnet

    Is that all that I'm missing?
    Thanks!
     
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