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Falling monkeys! (Projectile motion problem)

  1. Oct 27, 2009 #1
    1. The problem statement, all variables and given/known data

    http://img202.imageshack.us/img202/3459/phys.png [Broken]

    2. Relevant equations

    [tex]\Delta[/tex]Y=VoYt+1/2gt2

    3. The attempt at a solution

    Rearranging the equation (using [tex]\Delta[/tex]Y=h), I get [tex]\sqrt{}2h/g[/tex] which, from what I understand, means it takes [tex]\sqrt{}2h/g[/tex] seconds for the monkey to reach the point at which the coconut was thrown. My problem is moving on from here. All I know is that the monkey is at the original height of the coconut and the coconut is some portion of b from it's starting point (for what it's worth, my guess is 9, but I'd rather not lose points that I don't have to trying to guess). Where should I go from here?

    Thanks!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 27, 2009 #2

    rl.bhat

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    Homework Helper

    If the monkey catches the ball at a distance y from the ball, for monkey
    Δy = h + y = .....?.......(1)
    For the ball
    y =.........? (2)
    Solve these two equations to find t.
     
  4. Oct 28, 2009 #3
    For monkey
    ΔY = h + y
    ΔY=1/2gt2+Vimt+1/2gt2
    h is 1/2gt2, y is Vimt+1/2gt2 (Vim being the monkeys velocity after falling h meters.)

    For ball
    ΔY = y
    ΔY = Vibt+1/2gt2

    ΔY = ΔY
    1/2gt2+Vimt+1/2gt2=Vibt+1/2gt2

    And now I'm lost again. I tried figuring out the monkeys velocity once it reached the original height of the ball (a=Vf-Vi/t) and got
    V=g[tex]\sqrt{}2h/g[/tex], put that into the monkey equation and got ΔY=g[tex]\sqrt{}2h/g[/tex]t+2(1/2gt2), simplifying to ΔY=g[tex]\sqrt{}2h/g[/tex]t+gt2. I tried to set the two equations equal to each other, getting Vibt+1/2gt2=g[tex]\sqrt{}2h/g[/tex]t+gt2. From here I'm not sure what to do - I tried to find what t was equal to, but Vib and the two degrees of t's (t and t2) are making it rather difficult. I've tried rearranging twice and got a different answer each time. Any suggestions on what I'm doing wrong, or maybe where to start for rearranging?
     
  5. Oct 28, 2009 #4
    Please help? Someone?
     
  6. Oct 28, 2009 #5

    rl.bhat

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    Homework Helper

    Your equation for monkey is wrong. Initial velocity of the monkey is zero.
    In time t, monkey travels
    h + y = 1/2*g*t^2.--------(1)
    For Ball, the initial velocity is in the upward direction.
    So y = -vo*t + 1/2*g*t^2.-------(2)
    Find (1) - (2).
     
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