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Motion in Two Dimensions-Projectile off cliff

  1. Sep 15, 2011 #1
    1. The problem statement, all variables and given/known data
    A student stands at the edge if a cliff and throws a stone horizontally over the edge with a speed of 18.0m/s. The cliff is 50.0m above a flat, horizontal beach.
    a.) What are the coordinates of the initial position?
    b.)What are the components of the initial velocity?
    c.) Write the equations for the x- and y- components of the velocity of the stoned with time.
    d.) Write the equations for the position of the stone with time, using coordinates.
    e.) How long after being released does the stone strike the beach below the cliff?
    f.) With what speed and angle of impact does the stone land?

    2. Relevant equations
    I understand some, but am getting confused with the individual components of x and y.

    3. The attempt at a solution
    We were given a picture (attached)
    for a.) I decided to let the point where the rock would start at to be the origin (0,0).

    for b.) I knew the x component=18.0 m/s and y= 0m/s at the start.

    I know gravity= -9.8m/s and my Dvertical=-50 m. I also know that ViVertical=0m/s...

    for e.) I was able to find the time by using Dvertical=Vivertical(t)+(1/2)gt^2... I got t as 3.19 seconds.

    What do I do for c, d, and f though? Any help would be tremendous!

    Attached Files:

  2. jcsd
  3. Sep 15, 2011 #2
    For c. use an equation of motion in the y direction ans use an equation of motion in the x direction.
    You will have different initial velocity values etc..

    For d, key words.
    Equation, position (displacement), time.
    Do you know of any equation like this?

    For F, find the final velocity of the stone, in both X & Y directions. You will then have something like (aX - bY)
    You can then use trigonometery to solve the angle.
  4. Sep 15, 2011 #3


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    Staff: Mentor

    I note that the attached image indicates an origin for the coordinate system at the base of the cliff (the "O" mark). You might want to consider if this will make a difference for your answer submission.
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