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Homework Help: Help with kinematics

  1. Sep 17, 2007 #1
    1. The problem statement, all variables and given/known data

    A sailboard is sailing at 6.5 when a gust of wind hits, causing it to accelerate at 0.48 at a 35 angle to its original direction of motion.

    If the acceleration lasts 6.3 , what is the board's net displacement during the wind gust?

    2. Relevant equations

    Ok so far, I have drawn all of the motion graphs.
    So I got

    X Y

    X_0= 0m Y_0= 0m
    X_F=? Y_F=?
    V_0x= 6.5m/s v_oy=0m/s
    V_fy= 6.5m/s v_fy=?
    a= 0 m/s^2 a= .48m/s^2
    t= 6.3secs t=6.3secs

    3. The attempt at a solution

    And assuming those are correct. I got v_fy= 4.55 m/s by using 6.5tan35 = v_fy

    then I used this equation: x=x_0+v_ot+(1/2)at^2 and got

    X_f= 40.95m
    Y_f= 9.5m
    And then I added them together and then its 50.45m??? Is this correct, because online it said it was wrong?

    Thanks for helping!
  2. jcsd
  3. Sep 17, 2007 #2


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    Homework Helper

    suppose it's initially moving eastbound at 6.5m/s. ie: northbound velocity = 0.

    so acceleration 0.48m/s^2 east 30 degrees north.

    What is the component of acceleration in the east/west direction?

    What is the component of acceleration in the north/south direction?

    So you can divide the problem into the east/west part (to get the displacement east/west), and the north/south part (to get the displacement north/south)... and work them separetly... each part is a uniform acceleration problem.
  4. Mar 7, 2010 #3
    Need help with kinematics

    I figured out this problem:

    You step off a cliff 30 meters high.
    A. How long will it take to hit the water below?
    t^2= 6.122
    t= 2.47

    B. What is your velocity (mph) when you hit the water?
    Vty= Voy-9.8t
    Vty=-24.25 m/s = 54.223 mph

    Can anyone help me solve this one, based on the above problem?:

    2. How high would the cliff have to be in 1. above if your velocity hitting the water was 100 mph?

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