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Energy,mass problem

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  1. Aug 29, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the mass of the object which is being pulled by 40 hp engine with a constant speed 15 m/s (μ = 0.15)
    2. Relevant equations
    P=Fv
    F=μN

    3. The attempt at a solution
    I got about 1,350 Kg for the answer but I don't know why P=Fv( It is just included in the problem )
    First, I tried to figure how much force do I need to pull this object with P=Fv.
    29,840 J/s=F(15 m/s)
    I got F about 1940 N
    Now, I knew that I need 1940 N to pull this object, I use ΣF(system)=F(being pull)-F(friction)
    1940 N = (m)(a)-(μ)(m)(g)
    1940 N = 0-(0.15)(m)(9.8)
    m≈-1,350 Kg but a mass cannot be negative so the answer is 1,350 Kg
     
  2. jcsd
  3. Aug 29, 2016 #2

    SteamKing

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    Staff Emeritus
    Science Advisor
    Homework Helper

    You should draw a diagram for this problem.

    The tension in the rope which is doing the pulling is counteracted by friction. Your F(being pull) ≠ (m)(a), since a = 0 yet F(being pull) must be > 0.
     
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