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Force Exerted on an object

  1. Oct 20, 2015 #1
    1. The problem statement, all variables and given/known data
    The force exerted on a certain object varies with the object's position according to the function Fx(x)=ax^2+bx^3 where a = 3 N/m^2 and b = -0.50 N/m^3 .

    What is the work done on the object by this force as the object moves from x=−0.40 m to x = 2.0 m?


    2. Relevant equations
    W=F*x


    3. The attempt at a solution
    Ok, I know that the answer is 6.1 J, I just don't know how they arrived at that conclusion. My attempt:
    Fx(x)=(3)(-0.4)^2+(-0.5)(-0.4)^3 =0.512
    Fx(x)=(3)((2)^2+(-0.5)(2)^3=8

    Then I subtracted those two numbers to get 8-0.512=7.488 J
    That's kind of close, but not quite. What am I doing wrong?
     
  2. jcsd
  3. Oct 20, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    What you've done is calculate the value of the force at the two endpoints. Fx(x) is the value of the force as a function of x.

    What's the definition of work? Hint: Since the force varies with position, you'll need a bit of calculus to find the work done.
     
  4. Oct 20, 2015 #3
    It makes sense now. Thank you so much!!
     
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