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Please help! circular motion/ centripetal acceleration and more!

  1. Feb 10, 2009 #1
    1. The problem statement, all variables and given/known data

    Ok, I am a straight A student in math so you think Physics would be easy right? Not exactly. I really need someone to explain this stuff to me. Its probably really easy if it was explained to me correctly but my teacher is not the best when it comes to breaking things down. so here are SOME of the questions that I am having problems with.

    - A zoologist standing on a cliff aims a tranquilizer gun at a monkey hanging from a distant tree branch. The barrel of the gun is horizontal. Just as the zoologist pulls the trigger the monkey lets go and begins to fall. Ignoring air resistance, will the dart hit the monkey? Explain.

    - A long jumper leaves the ground with a speed of 6.8 m/s at an angle of 34 degrees. How far did she jump?

    - Mr. B swings a 3.0 kg mass at the end of a 2.3m string in a horizontal circle to demonstrate centripetal acceleration to a class. If the string can withstand a tension of 80N, at what speed can he swing the mass before risking a lawsuit?

    - A car is rounding a curve with a radius of 12 m at 8.2 m/s when it hits a slippery patch. What is the minimum coefficient of static friction between the car and the slick patch of road that will allow the car to round the corner safely?

    2. Relevant equations

    mabe these?

    a=v squared/r

    a=4 pie squared r/T squared

    F=4 pie squared rm/T squared

    3. The attempt at a solution

    I dont really know where to start? Or what equations to use, or if these are even the right equations?

    ANY help would be appreciated!!
    Thank you!
  2. jcsd
  3. Feb 10, 2009 #2

    Chi Meson

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    Too many questions. You are asking us to teach you a course in projectile motion and circular motion.

    For the first one, do a google search for the "monkey in the tree" experiment. It's a classic projectile motion problem. It's probably been answered here a dozen times at least.

    The second is a standard projectile motion problem. Crack open your textbook to that section and read it.

    Third is a simple circular motion problem. The string supplies the centripetal force to the mass. Centripetal force has simple formula. The maximum tension in the string determines the maximum centripetal force, and therfore the maximum speed.

    Last is a slightly harder circular motion problem. Friction supplies the centripetal force. Friction here is µmg.
  4. Feb 10, 2009 #3
    Ok so for the second one do I just set up X Y components? X: vox = vocos(theta) and Y: voy = vosin(theta)? And on the 3rd I use a = v^2 / r right?
  5. Feb 10, 2009 #4

    Chi Meson

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    On the third (and fourth) combine centripetal acceleration (what you have shown) with mass to get centripetal force. Newton's 2nd law, F=ma, right? so F=(mv^2)/r
  6. Feb 10, 2009 #5
    okay. Thank you very much! I appreciate your help.
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