1. Not finding help here? Sign up for a free 30min 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!

Simple work-energy problem

  1. Oct 13, 2004 #1
    A force of 5N acts on a 2 kg object that starts from rest. When the force has been acting for 2 s, the rate at which it is doing work is:

    Here's how I tried to solve it.

    Solve for acceleration, which I assumed was constant.

    Code (Text):

    a = F/m = 5N / 2kg = 2.5 m/s/s

    Then use the displacement equation to find the distance traveled.

    Code (Text):

    x = xo + (vo)(t) + (1/2)(a)(t^2)
    x = 0 + 0 + (1/2)(2.5 m/s/s)(2s)^2
    x = 5m

    Work = F * x = 5N * 5m = 25 J

    Power = Work / t = 25J / 2s = 12.5 W
    However, the only possible answer choices are:
    a) 5W b) 10W c) 25W d) 50W e) 75W

    Where am I screwing up?
  2. jcsd
  3. Oct 13, 2004 #2
    [tex]P=25\ W[/tex]
    You formula for power can't be used in this case because P is not constant for P depends on how long the force acts on the object.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Simple work-energy problem