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Homework Help: Conservation of mechanical energy ?

  1. Apr 2, 2008 #1
    conservation of mechanical energy ???

    i found this tricky since i would usually use something like v^2=u^2+2as but i dont have enough variables this time so I don’t even know which direction to go

    a stone is thrown upwards with u=20m/s. use conservation of mechanical energy to find out how huigh it will go?

    Oh I was told in a similar question earlier to take g as -10m/s^2 im not sure if I need this for this question

    Thanks very much to anyone who take the time to help me
  2. jcsd
  3. Apr 2, 2008 #2
    You don't need to(and are told NOT to, and to instead use conservation of energy) use those equations, however you still could as you were given initial velocity, and you know acceleration is g, like always, you would probably have to make a system of equations

    However what you're sposed to do is say "oh I know its initial kinetic energy is 1/2mv^2, and I know at its highest point it will have no KE and nothing but gravitational potential energy, and I know that its total energy at any given point will need to equal its initial energy"
  4. Apr 2, 2008 #3
    thank you

    i can see how stupid ive been, i should have a problem now
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