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Homework Help: Two dimensional physics problem

  1. Jan 22, 2004 #1
    In a snowball fight 2 snowballs are thrown in the same direction, but one is thrown 70.0 degrees with respect to the horizontal and the other is thrown some arbitrary distance lower. they both are thrown with a speed of 25.0 m/s.

    At what angle should the one that is thrown lower be to arrive at the same point as the one that was thrown at 70.0 degrees?

    How many seconds later should the lower thrown snowball be thrown to arrive at the same time as the higher one.

    resolving into x and y components for the first one i get.

    x initial = 0
    x final =?
    v initial = 25.0cos(70.0)
    v final = 0 m/s
    a = 0 m/s^2

    y initial = 0
    y final = ?
    v initial = 25.0sin(70.0)
    v final = 0m/s
    a = -9.80m/s^2

    then i get lost...


  2. jcsd
  3. Jan 22, 2004 #2

    Doc Al

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    Staff: Mentor

    What makes you think "v final = 0 m/s"?
  4. Jan 22, 2004 #3
    i figured that when the snowball made contact with the target it's velocity would be 0.
  5. Jan 22, 2004 #4


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    As someone who has been hit often by snowballs before, I can reassure you that as the ball hits you, it is definitely not stationary. (You are confused with collision modelling here, I think. The velocity after it hit is presumeably zero. But not as it hits/just before it hits.)

    What you want to do is to use the uniform acceleration equations in each case to work out an expression for time taken in each case for the ball to fall to the ground, and then insert this to find out the horizontal distance travelled for each, and equate the two distances to find the angle.
  6. Jan 22, 2004 #5
    i am kinda confused. this is my first quarter in physics and i seem to confuse the moment before collision and the stationary component of the final velocity. i guess that is why i was enlisting the help of people that are far more superior in their understanding of physics then myself...

    i'll give what you said a shot.


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