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Projectile motion

  1. Oct 12, 2003 #1
    I just need alittle help on getting started with just the formulas.
    There are just two question.

    1) A baseball thrown at 100.8 mi/hr. If the pitch were thrown horizonally with this velocity how far would the ball travel vertically by the time it reaches home plate 60.0 ft away?

    Do i need to worry about the time it takes?

    2) If a student stands at the edge of a cliff and throws a rock horizonally over the edge with a speed of 18.0 m/s, The cliff is 50 m above a flat. How long after being released does the rock strile the beach below the cliff? With what speed and angle of the impact does it land.

    I do know the the angle = tan-1 (Vy/Vx)

    I am just struggling a bit on these two.

    Thanks
     
  2. jcsd
  3. Oct 12, 2003 #2

    HallsofIvy

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    Well, yes, you do. You know the horizontal velocity and that there is (neglecting air resistance) no horizontal acceleration so it should be easy to determine the time a ball moving at 100.8 mi/hr takes to travel 60.0 feet (you might want to convert that speed to ft/sec). You know that there is no initial vertical speed and the vertical acceleration is -32.2 ft/sec2.

    Once again, you know that the horizontal speed, 18.0 m/s and that there is no acceleration vertically. You know that there is no initial vertical speed and the vertical acceleration is -9.8 m/s2. You should be able to write down the horizontal and vertical speed at any time t as well as the horizontal and vertical distance from the initial point. Since the rock has to go down 50 m in order to hit the beach, you need to find the time required for the vertical
    distance to be -50- then use that to find the speed and angle.
     
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