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Homework Help: Determining Velocity with Projectile Motion

  1. Oct 31, 2007 #1
    1. The problem statement, all variables and given/known data
    Ok Im having slight trouble with a homework problem. An arrow was launched at an angle, and hit a balloon that was 150m away and 100m up. I used my distance equations along with initial velocity to calculate the two angles that can be used to hit the balloon, but I'm stuck on the next part. I used t=dx/vx to solve for time, and now I need to solve for the velocity when the arrow hits the balloon. I'm sure it's a simple problem but I'm stuck!

    Initial Velocity=60m/s
    Distance from 0=150m
    Height in Y direction=100m




    I used the four equations above to solve for the angle(s). Then put in the velocities to solve for time. How do I solve for velocity when the arrow hits the balloon?
  2. jcsd
  3. Oct 31, 2007 #2
    You know vertical displacement, you can calculate Vy. Vx will remain constant.
  4. Nov 1, 2007 #3
    Should I use Vy=Voy+at?
  5. Nov 1, 2007 #4


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    Science Advisor

    Yes, if you know V0y and t, you can use that to solve for Vy. You already know that Vx= V0x.
  6. Nov 1, 2007 #5
    Yes, I know that Vx is constant throughout the motion. So using Vy=Voy+at, I can solve for the velocity at any one point in time at a certain height?
  7. Nov 1, 2007 #6
    You are given height, acceleration due to gravity, and initial Vy. Think of some other s-u-v-a-t formula which could give you final Vy at a given height more quickly!

    1. You will get two Vy at a particular heght.. I hope you can decide which one to take!
    2. From Vy thus obtained and Vx, you can, of course, obtain final velocity.
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