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Homework Help: Hooke's Law Problem Set with Word Problems

  1. Feb 14, 2012 #1
    Hello all,

    I am currently working at a problem that is (seems) simple at calculations but I am puzzled by the word problems.

    The problems are:

    1. A spring powered projectile launcher contains a spring with:

    k=300 N/m

    The spring is compressed by 15.0 cm.

    a. How much energy is stored in the compressed spring?

    My answer is: 1/2 kx^2, and the answer is about 3.375J

    b. How fast would a 38 g projectile be traveling if it were shot by this projectile launcher?

    my answer is 13.3278 m/s

    So my question is: would using a lighter projectile provide more momentum or less? Prove the statement algebraically.

    Second question is: a truck sinks lower when you load it and it bounces slowly when it is loaded than when it is empty. Explain these phenomena using formulas.
  2. jcsd
  3. Feb 14, 2012 #2
    Please answer asap!
  4. Feb 14, 2012 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good.

    What do you think? Hint: What remains constant, regardless of the mass of the projectile?

    What do you think?
  5. Feb 14, 2012 #4
    I think the momentum would remain constant right?

    I don't really know about the second question but I have a somewhat guess:

    The more mass there is on the truck, the truck bounces less than it is not loaded. Or there will be no difference since the springs in a truck will compress..
  6. Feb 14, 2012 #5

    Doc Al

    User Avatar

    Staff: Mentor

    Whether the momentum changes is what you need to show. What remains constant for any projectile launched from this compressed spring?

    Pick one!

    The fact that a loaded truck sinks more should make sense from Hooke's law.
  7. Feb 14, 2012 #6
    how to show?
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