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: Energy and Speed

  1. Apr 5, 2005 #1
    With reference to the attached "energy versus distance graph" of two particles;

    a. What minimum speed (m/s) does a 100 g particle need at point A to reach point B?

    b. What minimum speed (m/s) does a 100 g particle need at point B to reach point A?

    Thank you.
     

    Attached Files:

  2. jcsd
  3. Apr 5, 2005 #2

    Galileo

    User Avatar
    Science Advisor
    Homework Helper

    Use conservation of energy. First find the minimum kinetic energy needed to go from A to B, then get the speed from that.
     
  4. Apr 5, 2005 #3
    In order to find the minimum kinetic energy, I think I have to find the total work done referring to a "Force vs Distance" graph. But, how can "Force" be found from a graph which is not linear?
     
  5. Apr 5, 2005 #4
    Work = [itex] \int F dx [/itex]

    Is this gravitational potential? In that case, its conservative, and you can ignore anything but the starting and ending points. You lost 2 Joules of PE to get from A to B, so you gained 2 Joules of KE.

    [tex] KE = 1/2 mv^2 [/tex]

    [tex] 2 = 1/2 (100g) v^2 [/tex]
     
  6. Apr 5, 2005 #5

    Galileo

    User Avatar
    Science Advisor
    Homework Helper

    In one dimension, any position dependent force is conservative (the potential (or total?) energy is already given as a function of the position).
     
  7. Apr 5, 2005 #6
    Isnt "position dependant force" part of the definition of "conservative force"? Say there was a resistance factor such as friction, the energy wouldn't be conserved then.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook