1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Work and Kinetic Energy problem

  1. Oct 26, 2008 #1
    A force Fx acts on a particle that has a mass of 1.5kg. The force is related to the position x of the particle by the formula Fx = Cx^3, where C = .50 if x is in meters and Fx is in newtons.

    a) What are the SI units of C?
    b)Find the work done by this force as the particle moves from x=3.0m to x=1.5m
    c)At x = 3.0m, the force points opposite the direction of particle's velocity(speed is 12.0m/s). What is its speed at x=1.5m?

    For A:
    Isn't C just a constant? What units is this in?

    For B:
    I have to integrate Fx and the integral of F(x)dx = x^4/4
    Since C is a constant I can put it in front of the integral so is 1/4 C x^4
    When I integrate shouldn't there be a + K? 1/4 C x^4 + K
    X1 = 3.0 and X2 = 1.5
    Plug in and solve?

    For C:
    Using answer from Part B = Work total
    Work total = 1/2 M Vf^2 - 1/2 M Vi^2
    where Vi = 12m/s?
  2. jcsd
  3. Oct 26, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Just because C is a constant doesn't mean it has no units. Hint: For any equation, the units on each side must match.

    Since you are doing a definite integral (between limits) the integration constant goes away. Just evaluate between those limits.

    Good. Use the work-energy theorem.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook