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Homework Help: Projectile motion

  1. Mar 16, 2005 #1
    he everyone again!!!!
    today, i just got a lab for physics. I have two days to really examine that gun. the teacher will give me an angle that i should aim the gun, and a cup. I should know the distance between the gun and the cup so that when i launch the ball, it will go inside the cup...
    first of all, i looked for "new" gravity, since there is air friction when the ball is launched, and i found that is 9.7m/ss , then I looked for the Initial velocity, i launched the ball vertically and i counted the time that took the ball to go upwards til it stops, then i counted the distance fron where it was lunched and where it stoped...after all, i found that the initial velocity is 6.69 m/s
    Now, i am confised, first of all, can anyone tell me how is the angle of the gun related to the distance between where the gun is and where the ball landed after it was launched?????
    i tried to look for the time that it takes vertically for the ball when it is launched, i think i found .69sec that means that in .69 sec, the ball will go like v=d/t, (should i use the initial velocity for v???) if so, i found d=4.62m....
    where do i have to use the angle...
    also, i was very confused, so i decided to the a graph (the teacher said he is gonna give me an angle to aim the gun between 30 and 60 degrees) so i launched the ball at 30,35,40,45,50,55,60 degrees, and i counted the distance the ball traveled, but i don t think that s a great idea since i ll have to launch the ball so it will go into the cup which is like 6cm of diameter, and to do that i have to be more accurate...
  2. jcsd
  3. Mar 18, 2005 #2
    You need to use the angle to split up the initial velocity into components. I am not quite sure what you did to come up with the distance that you did.

    The y component of the velocity experiences a constant acceleration. This allows you to find the time the ball is in the air. Then, using the x component and the time you can determine the distance it will travel.

    Will the cup be at the same height as the gun?

    Hope this helps.

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