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Homework Help: Projectile Motion escalator

  1. Oct 14, 2013 #1


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    1. The problem statement, all variables and given/known data

    You are at the mall on the top step of a down escalator when you lean over laterally to see your 1.8 m tall physics professor on the bottom step of the adjacent up escalator. Unfortunately, the ice cream you hold in your hand falls out of its cone as you lean. The two escalators have identical angles of 40 degrees with the horizontal, a vertical height of 10 m. Will the ice cream land on your professor's head? Explain. If it does land on his head, at what time and at what vertical height does that happen? What is the relative speed of the ice cream with respect to the head at the time of impact?

    2. Relevant equations


    3. The attempt at a solution

    I'm able to find time:

    -4.905t^2-0.25115t+10.0 = 0.25115t+1.8
    -4.905t^2-0.51423t+8.2 = 0
    (-4.905t^2-0.51423t+8.2)*-1 = 0 * -1
    4.905t^2+0.51423t-8.2 = 0

    t = -b +/1 sqrt ( b^2 - 4 ac) / 2a
    t = ((-0.51423 +/- sqrt( (0.51423)^2 - 4(4.905) (-8.2) ) / (4.905)*2
    t = (-0.51423 +/- 12.694425)/9.81


    t = -13.20866/9.81
    t = -1.35


    t= 12.18019525/9.81
    t= 1.24


    I'm not sure how to find the vertical height and relative speed with respect to the head at the time of impact. Insight would be greatly appreciated, thank you. :)
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 15, 2013 #2


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    I know we're supposed to make use of a Galilean transformation, but I'm not sure how...
  4. Oct 15, 2013 #3
    [STRIKE]the question gave you the information, that both professor, ice-cream with student is on escalator. Its pretty safe to assume they have same horizontal velocity (magnitude). So, the answer is yes it will land on professor's head!!!....This should give you some insight!!![/STRIKE]

    I guess I overlooked some things

    what is this value (0.400)????........You haven't mentioned anything about it in your question.
    Last edited: Oct 15, 2013
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