Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Water Rocket

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data
    Hi, guys.
    I did a project but questions are killing me right now.
    I was going all the tutorials but I really have no idea.
    What we did was water rocket project.
    Here are the data
    Ttotal - avg. 9.96 sec.
    Avg. Apogee - 2.94 sec.


    2. Relevant equations



    3. The attempt at a solution


    I need to find the v initial, ymax, and the maximum range.
    Here is how I did it

    For Vinitial
    DeltaY(0) =(Vinitial)(5.88)+(1/2)(-9.8)(5.88)^2
    Vinital = 28.8m/s
    5.88sec comes from avg. apogeeX2 ------> (2.94)(2)

    For Ymax,
    Ymax= (Vinital)(time)+(1/2)(-9.8)(time)
    (28.8)(2.94)+(1/2)(-9.8)(2.94)^2
    = 42.3 m

    For maximum Range,
    I found out that cos 45 will give me maximum range so

    Range=(Vinital)(cos45)(time)
    (28.8)(cos45)(5.88)
    = 119.7 m

    Lastly, my teacher asked, "What role does the water play in making the rocket move?"
    He also asked for relevent formulas and a diagram illustrating the forces.
    Only thing we learned so far are Horizontal Projectil motion and free fall.
    I do not think we ever learned this.
    Can you please help me with this? Ive been working for entire day!!
    Thanks guys.
     
    Last edited: Nov 2, 2008
  2. jcsd
  3. Nov 2, 2008 #2
    Oh, I realized I had to put what I did.
    here is what I did..
    for Vinitial,
    I did
    deltaY=(Vinitial)(5.58)+(1/2)(-9.8)(5.88)^2
    and got Vinitial=28.8m/s.
    5.88 comes from avg. apogee= 2.94X2=5.58

    For Ymax,
    I did
    Ymax = (28.8)(2.94)+(1/2)(-9.8)(2.94)^2
    Ymax = 42.3 m

    Lastly, for Range
    Since Range max, I found that cos 45 will give me maximum range
    So,
    Range=(Vinital)(cos45)(time)
    (28.8)(cos45)(5.88)
    Range=119.7m.

    Here is how i did it.
    But honestly,
    on the last problem with "what role does the water play in making the rocket move?"
    I abs. have no idea.
    Thanx guys.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook