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 done by a varying force of a block

  1. Sep 29, 2010 #1
    1. The problem statement, all variables and given/known data
    A block with mass 5.00kg, moves along the x-axis with zero friction. The block experiences a net force Fx that varies with it's position x. When x=0, v (initial speed) is equal to 2.0 m/s

    Find the work done on the block when it is displaced from x=0 to x=8

    What is the final speed at x=8

    This is not the original problem statement ... I had to translate it to English in order to post it here. :p

    Se attached image for the graph of the relationship between the force and displacement.

    2. Relevant equations

    3. The attempt at a solution
    Calculated the area in the trapezoid, and subtracted the area of the triangle. 30J-5J=25J, I think this is right answer?

    Then I used the relation between work and kinetic energy

    W=delta K=(1/2)m*v_f^2 - (1/2)m*v_i^2
    where the subscript i and f stands for initial and final speed

    Solved this for v_f and got the answer 3 m/s

    Are these answers correct? Unfortunately, I don't have the answers, since this is a problem I got from my physics professor, not from the textbook.

    Thanks in advance. :)

    Attached Files:

  2. jcsd
  3. Sep 29, 2010 #2
    Yes, you calculated the area under that curve correctly and applied the work energy theorem (work=change in kinetic energy) to calculate the final velocity at x=8. Everything seems fine to me.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook