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!

Double KE, what happens to velocity

  1. Oct 21, 2004 #1
    if you double the KE, by what factor does the speed increase? and vice versa

    i am a little lost
  2. jcsd
  3. Oct 21, 2004 #2


    User Avatar
    Homework Helper

    The speed will increase by [itex] \sqrt(2) [/itex]

    Use the equation

    [tex] K = \frac{1}{2}mv^2 [/tex]

    If the speed increases twice

    [tex] K = \frac{1}{2}m(2v)^2 [/tex]

    [tex] K = 4 (\frac{1}{2}mv^2) [/tex]

    [tex] K = 4K [/tex]

    Kinetic energy will increase four times.

    Now if the kinetic energy increases four times

    [tex] v = \sqrt{\frac{2K}{m}} [/tex]

    [tex] v =\sqrt{\frac{(4)2K}{m}} [/tex]

    [tex] v = \sqrt{4} \sqrt{\frac{2K}{m}} [/tex]

    [tex] v = 2 \sqrt{\frac{2K}{m}} [/tex]

    [tex] v = 2v [/tex]

    The speed will increase two times.
    Last edited: Oct 22, 2004
  4. Oct 22, 2004 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    To clarify Cyclovenom's reply (i.e. to avoid statements like [tex] K = 4K [/tex], which implies that [tex]K=0[/tex]), try this.

    The relation between kinetic energy and speed is

    To double the speed, think [tex] v_\text{new}=2 v_\text{old} [/tex].
    Since you're probably assuming that the mass is unchanged, [tex] m_\text{new}=m_\text{old} [/tex].

    &={\color{red}4} K_\text{old}\\

    You can try this technique to answer your questions.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?