Energy Conservation & Potential Energy Spring/Friction Problem


    A 0.80-kg block is held in place against the spring by a 67-N horizontal external force. The external force is removed, and the block is projected with a velocity v1 = 1.2 m/s upon separation from the spring. The block descends a ramp and has a velocity v2 = 1.9 m/s at the bottom. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction is 0.39. The velocity of the block is v3 = 1.4 m/s at C. The block moves on to D, where it stops. In Fig. 7.4, the force constant of the spring is..


    2. Relevant equations

    K1 +U1 +W other = K2+ U2.. ect .. U2=0.5kx^2 .. K1=(0.5)mv^2

    3. The attempt at a solution

    I've tries solving the problem with the equation above but I really just don't know where to start especially since there are no units of distance given.. Can someone lead me in the right direction please?
    Last edited: Mar 6, 2011
  2. jcsd
  3. tiny-tim

    tiny-tim 26,016
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    Hi Help1212! :smile:


    I assume you can find kx and kx2/2 ?

    ok, then k = … ? :wink:
  4. euhh... i'm still a little do i find k if I don't know x?
  5. tiny-tim

    tiny-tim 26,016
    Science Advisor
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    x is twice kx2/2 divided by kx :wink:
  6. hmm. well when I move around the equation i get k=2[0.5(mv22)/x2

    from the assumption that K1 + U1 = K2 + U2

    Am i going in the right direction??
  7. tiny-tim

    tiny-tim 26,016
    Science Advisor
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    can you find kx and kx2/2 ?

    if so, what are they?

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