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Homework Help: Projectile Motion Ball Calculation

  1. Sep 12, 2006 #1
    A question from my pre-unit test review

    A ball is projected from point A with an intial velocity Vo, which is perpendicular to the incline shown. Knowing that the ball strikes the incline at B, determine the range R in terms of Vo and β.

    Diagram can be seen here:

    http://img146.imageshack.us/img146/3231/projectile001xu5.jpg [Broken]
    I drew the delta X/Y, and 90-β

    I did some calculations(very messy), still confused about it though

    For typing purposes I used V1 for Vo
    V1y = V1sin(90-β)
    V1x = V1cos(90-β)

    First I tried to find time:
    y = V1yt + 1/2ayt²
    0 = V1sin(90-β)t + 1/2(-9.8)t²
    V1sin(90-β)t = 4.9t²
    t = V1sin(90-β) / 4.9

    Horizontal range:
    x = V1xt
    x = [V1cos(90-β)] [V1sin(90-β) / 4.9]

    Finding R:
    cosβ = X / R
    cosβ = [V1cos(90-β)] [V1sin(90-β) / 4.9] / R
    cosβ = [V1cos(90-β)V1sin(90-β) / 4.9R]

    This looks really messed up can someone check my work please.....if its too messy to read I'll write it out on request and scan it
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Sep 13, 2006 #2
    Please, need a reply
  4. Sep 13, 2006 #3

    Doc Al

    User Avatar

    Staff: Mentor

    You are finding the time when y = 0. Why?

    This seems to be the x-coordinate when y = 0. Not what is needed.

    Here's what I would suggest: Express y and x as functions of time. Combine this with an equation which relates y & x along the incline. (What's the equation of a straight line?)
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