1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculate time traveled from launch to land

  1. Sep 19, 2010 #1
    1. The problem statement, all variables and given/known data
    So, this is pretty easy and simple, I am just missing something obvious here I am pretty sure. This stems from a question I asked earlier tonight.
    Calculate the time it took from launch to land, given a velocity of 30.197m/s, and a distance traveled of 85m. (other irrelevant data: Object was initially launched at 33 degrees. Refer to https://www.physicsforums.com/showthread.php?p=2890328#post2890328 for more info)


    2. Relevant equations
    Perhaps, X=Xo+Vot+.5at^2 ???


    3. The attempt at a solution
    So, I would use the formula X=Xo+Vot+.5at^2, correct? But then, I get a bit confused...
    -.5t^2=Vot-X
    divide by t
    -.5t=Vo-X
    t=-2(Vo-X)
    but that is incorrect, I think... SO I dunno... Help, please... Thank you

    Oh, wait... Am I maybe just way over-analyzing this? Would it be as simple as Distance/Velocity=Time? Therefore, V=30.197m/s , and D=85m, so 85/30.197=2.815s. But that seems a bit short. The empirical data is 4s (we must find the percent error), that is quite a large percent error...
     
  2. jcsd
  3. Sep 19, 2010 #2

    rl.bhat

    User Avatar
    Homework Helper

    In the horizontal direction there is no acceleration.

    s = vo*cos(theta)*t.
     
  4. Sep 19, 2010 #3
    Which is why I excluded 'a' when simplifying the equation, because a=0. Let me try that equation. Hmm... that seemed to yield a much more reasonable answer, 3.356s. That seems to be correct. Yeah, I get it now. It makes sense. Funny how things can just click and then you get it. Thank's for the help, I knew that it was really simple, I was just making it complicated.

    Do you think you could help me really quickly with one more? Sorry.
    Q: Find the initial velocity, when the object is shot at 70 degrees and took 6.5s to land. (hint: look at the y direction first this time)

    Now, I know that there is the method of dividing it up into components of x and y, however I did not quite understand that. When calculating the initial velocity, given distance traveled and degree, I used Range = v02sin2θ/g which worked great (refer to https://www.physicsforums.com/showthread.php?p=2890328#post2890328 ), however, I don't know if that can apply to this too... Sorry, but physics is really confusing me at the minute
     
  5. Sep 20, 2010 #4

    rl.bhat

    User Avatar
    Homework Helper

    Q: Find the initial velocity, when the object is shot at 70 degrees and took 6.5s to land. (hint: look at the y direction first this time)

    If it lands on the ground, vertical displacement y is zero. Vertical component of the velocity is vo*sinθ.
    Use the equation
    y = vo*sinθ* - 1/2*g*t^2

    Substitute the values and find vo.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook