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 Question - Is something missing?

  1. Jun 26, 2008 #1
    1. The problem statement, all variables and given/known data
    Calculate the work done accelerating a 2.0 kg object from 2.0 m/s to 3.0 m/s.

    mass=2.0 kg
    Initial Velocity= 2.0 m/s
    Final Velocity= 3.0 m/s

    2. Relevant equations
    Work=applied force x displacement

    3. The attempt at a solution
    Correct me, if I am wrong, but don't I need a bit more information to answer this question? This was all the information given to me.
  2. jcsd
  3. Jun 26, 2008 #2


    User Avatar
    Homework Helper

    Hi Sabellic,

    No, that's all you need. The equation you listed is true; however, there is another equation that involves work and velocity. What is it?
  4. Jun 26, 2008 #3
    Hmmmm. I don't know. The only thing that I can conjure up is that the work can be equivalent to (mass/acceleration) * (final velocity^2 - initial velocity^2)/2 * a^2

    But that doesnt work because i dont have the acceleration.
  5. Jun 26, 2008 #4


    User Avatar
    Homework Helper

    That's so close! But it needs to be:

    (mass/acceleration) * (final velocity^2 - initial velocity^2)/2 * a

    and so the accelerations will cancel.

    Then notice that what you have left is:

    (1/2) m vf^2 - (1/2) m vi^2

    Does that look more familiar? What are those terms? Once you have that, you will have the important equation that you need to know.
  6. Jun 26, 2008 #5
    Oh God you're right. I wrote (mass/acceleration) instead of mass * acceleration. So yes, they would cancel out. Thanks a lot for this. So it will be 5 Joules, I think.
  7. Jun 26, 2008 #6


    User Avatar
    Homework Helper

    That's good, but you don't want to have to derive that important formula every time. The way to think about it is

    total work = change in kinetic energy

    (where total work includes all conservative and non-conservative work).

    Since kinetic energy is (1/2) m v^2, you could write down the relation you need right away.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook