1. Limited time only! Sign up for a free 30min personal 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!

Find v(t) the velocity vector of a projectile given a(t).

  1. Sep 28, 2011 #1
    1. The problem statement, all variables and given/known data

    Suppose we have a projectile launched from an initial height of h ft with initial speed V0 ft/sec and angle of elevation theta. We will attempt to model air resistance by assuming acceleration vector given by...

    a(t)= (-.2)(V0)cos(theta)e^(-.2t)i-(.2)((V0)sin(theta)+160))e^(-.2t)j

    2. Relevant equations



    3. The attempt at a solution

    I know I need to integrate this equation, but I am not getting the correct value.
    The teacher gave us a hint that v(0)=(V0)cos(theta) i+ (v0)sin(theta) j
     
  2. jcsd
  3. Sep 28, 2011 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    θ is just a constant, so it should be easy to integrate a(t) .
     
  4. Sep 28, 2011 #3
    i component
    [PLAIN]http://www4b.wolframalpha.com/Calculate/MSP/MSP27119ha2d01ca4299bi000030d6c3af4h784902?MSPStoreType=image/gif&s=32&w=352&h=34 [Broken]

    j component
    [URL]http://www2.wolframalpha.com/Calculate/MSP/MSP477919ha2b5d070h1318000054ch856h732hh6ac?MSPStoreType=image/gif&s=16&w=442&h=34][/URL]
     
    Last edited by a moderator: May 5, 2017
  5. Sep 28, 2011 #4
    I can integrate it but the teacher said

    Find the velocity vector of the projectile (remember that v(0)= V0*cos(theta)i+V0sin(theta)j

    every time I integrate a(t) to get v(t) then plug t=0 I cannot get rid of the +160
     
  6. Sep 28, 2011 #5
    theta and V0 are constants
     
  7. Sep 28, 2011 #6
    anyone?? really need help on this
     
  8. Sep 28, 2011 #7

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    How did you get rid of your constants of integration?
     
  9. Sep 28, 2011 #8
    I did not get rid of the constants V0 and theta I just put them outside of the integral. I got a couple similar answers, but I did not understand the comment he put under the question. I am stiff confused on this problem
     
  10. Sep 29, 2011 #9

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Those are not constants of integration.

    When you find an anti-derivative there is a constant of integration, usually C, that is added to the result.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook