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Homework Help: Physics Motion Problem (Displacement)

  1. Mar 6, 2008 #1
    1. Hi, my question deals with displacement and given acceleration : A boy and a ball are at the top of a ramp. the ball rolls down accelerating at 0.2 m/s(squared). The boy chases after the ball 12 seconds later accelerating at 0.9 m/s(squared). The length of the ramp is 60 meters. Will the boy catch the catch the ball before the end of the ramp, if so what displacement/ time will it be at


    2. I was trying to use v2=v1 + aΔt, and manipulate it for the getting the time by after using the equation, Δd=v1Δt+0.5a(Δt)squared



    3. My attempt was by trying to divide the displacement by the acceleration and i think i got time(squared) so i square rooted that and than i plugged in the that time by the acceleration to get velocity at that time, and than calculating the displacement by multiplying the velocity by the time. I also tried to substitute the time/ displacement values into each other but i could not balance it out to solve it algebraically. I also tried graphing it and i got my answer somewhere around 15 seconds but i'm not allowed to graph

    Any Help would be appreciated.... Thanks
     
  2. jcsd
  3. Mar 6, 2008 #2
    the total length of ramp = 60 m
    So, s= 1/2(0.2)t^2 =0.1t^2
    after 12s s' = (0.1)(12)^2=14.4 m
    14.4+(0.1)t^2
    for the motion of boy
    s=1/2(0.9)t^2
    combine the equation, find t
    if 14.4+(0.1)t^2>=60 it is impossible
    <=60 , it is possible
     
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