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Acceleration question

  1. Jul 15, 2011 #1
    I've been trying to figure this problem out for a few hours now. Please, if you have helpful hints, help me out!

    You can see the problem here on page 7, the problem about the toy cricket: http://www.physics.princeton.edu/~mcdonald/examples/ph101_2006/learning_guide_ph101_2006.pdf

    A toy cricket is stuck to the floor with a suction cup which after a few moments releases to allow a spring to propel the cricket upward. The expanding spring accelerates the cricket over a distance of 0.01 m to point A, after which the toy travels freely to a maximum height of 1.00 m above the ground (point B).

    What is the net acceleration during the time the spring expands? Assume uniform acceleration.

    The answer is 970 m/s^2.

    I just do not know where to start. I assume we use x = (1/2)(acceleration)(t^2) but don't know enough of the variables to plug and chug.
  2. jcsd
  3. Jul 15, 2011 #2
    you have solved 1,2 parts
    so now you have speed when spring is completely expanded.

    for the accelerating motion you have final vel., initial vel. , height
    which newton eqn can be used to find acc.?
  4. Jul 15, 2011 #3
    Still confused...

    Aren't they asking for the acceleration when the spring remains on the ground? Once the spring gets to point A, it jumps up in the air. Am I picturing this incorrectly?

    For the question, I thought they wanted the acceleration for when it travels 0.01 meters and that the spring is fully expanded by the time it jumps off the ground at point A.
  5. Jul 15, 2011 #4
    You have to work this problem in a couple steps. First, find out the velocity at which the cricket has to travel in order to go from 0.01 m to 1.00 m when only gravity is exerting a force on it. I'll let you see if you can figure out the rest from there. :)
  6. Jul 15, 2011 #5
    omg you guys are geniuses...I just got it. physics is so difficult for me! thank u so much u guys
  7. Jul 15, 2011 #6

    no, the spring is expanding from A to C ... and then goes, under gravity effect, from C to B and then back.

    for A-C motion, it experiences gravitational force and also a spring force (which is not constant but here its given for the sake of simplicity).

    and then are asking acc. in A-C motion
    C-B motion will have acc. g

    Attached Files:

  8. Jul 15, 2011 #7
    You're welcome! Practice definitely makes perfect in physics.
  9. Jul 15, 2011 #8
  10. Jul 15, 2011 #9
    i am having to re-take physics next year..so im trying to improve during the summer! :) i hope practice DOES make perfect :))))))
  11. Jul 16, 2011 #10


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    Staff: Mentor

    I'd like to remind people of our rule that we give only hints, not complete solutions. (just in case you're wondering what happened to the most recent posts in this thread.)
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