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!

Kinetic Energy/Velocity problem (not sure what I'm doing wrong)

  1. Dec 5, 2007 #1
    1. The problem statement, all variables and given/known data

    A 10.89kg bowling ball moves at 3.46 m/s. How fast must a 40.3g golf ball move so that the two balls have the same kinetic energy?

    2. Relevant equations

    Kinetic Energy = (1/2)V^2

    3. The attempt at a solution

    I set plugged the information into the kinetic energy problem and set them equal to each other to solve for V.

    (1/2)(10.89kg)(3.46m/s)^2=(1/2)(.0403kg)(V^2)
    V=238.3 m/s

    Thats not the answer in the back of the book though, I'm not sure what I'm doing wrong.
     
  2. jcsd
  3. Dec 5, 2007 #2

    malty

    User Avatar
    Gold Member

    You may want to recheck that calculation, I did it and got 56.88 m/s, but then again I may also have to check mine :)
     
  4. Dec 5, 2007 #3
    Ahh I get that now, and thats the answer in the back of the book, I'm not sure how I was doing the algebra wrong, thanks:)!
     
  5. Dec 5, 2007 #4
    Hello,

    Your formula is off (you're missing the m), but it looks like you used the correct form in the calculation.

    Your calculation is off, you need to recheck. Are you sure your only squaring the velocity?

    Incidentally, another way to do this is to solve for the velocity of the golf ball before you substitute numbers in:

    [tex]\frac{1}{2}m_{b}{v_{b}}^2 = \frac{1}{2}m_{g}{v_{g}}^2 \Rightarrow m_{b}{v_{b}}^2 = m_{g}{v_{g}}^2 \Rightarrow \frac{m_{b}{v_{b}}^2}{m_{g}} = {v_{g}}^2 \Rightarrow v_{g} = \sqrt{\frac{m_{b}}{m_{g}}} \cdot v_{b}[/tex]

    Hope this helps.

    Edit: You solved it before I could get the LaTeX down :-) Good job
     
    Last edited: Dec 5, 2007
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?