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Homework Help: Help me ace my physics test tomorrow!

  1. Jun 27, 2005 #1
    I am looking over my study and have a few questions. How would I solve some of these questions?

    1) An ice skater moving at 12m/s coasts to a halt in 95m on an ice surface. What is the coefficient of friction between the ice and skates? QUESTION: is the formula to use for this always going to be -mew with little k = a with little x divided by g? Will the answer be -.077?

    2) A car exits from the expressway to a circular exit ramp that posts a maximum exit speed of 35mph (15.6 m/s). If the typical coefficient of static friction between tires and pavement is 0.4, what is the radius of the exit ramp? QUESTION: Is this the formula i need to use to solve this R=Vsquared/mew times g ? The answer I got is 62.018m. Am i doing this right?

    3) A pail of water is rotated in a vertical circle of radius 1m. What is the minimum speed of the pail at the top of the circle if no water is to spill out?
    QUESTION: Is this the right formula Vsquared=RG? The answer I got is 3.03 m/s(squared) Am I on the the right track with this one?

    Please help me do good on my test tomorrow. Any and all help would be greatly appreciated :smile:
  2. jcsd
  3. Jun 27, 2005 #2
    Hard to tell if its right without seeing the work, but these don't take alot of calculations, so....

    The answer is right. Also I would't say the formula is always going to be that.


    At a glance your answer is the acceleration, but the question is asking for the speed.
  4. Jun 27, 2005 #3
    in addition to previous comments:
    1) coeff of friction generally given with (+) number. so here μk=+0.077
    2) looks good. can you derive the formula which you stated?
    3) basic formula is (mV2)/R = mg
    so you're right that V2 = Rg
    or V = √(Rg) = √(9.8) = 3.13 m/sec
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