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Kinematics with projectile motion(2 questions)

  1. Sep 23, 2012 #1
    1) Jim decides to jump a gorge on his skateboard. The gorge is 50 m wide and jim has constructed a 1 m high ramp iclined at 30 degrees to the horizontal. If air resistance is neglected, calculate what speed Bart must reach if he is to land safely on the other side of the gorge.

    The answer is 23 m/s but I dont know how to get it.

    2) Jake has calculated that he can jump the jorge if the ramp is inclied to 45 degrees, and he attains a speed of 20 m/s. Will Jake make it? If not how much short of the other side is he when he drops below the level of the ground?

    The answer is no, and 9 m but i dont know how to get it.
     
  2. jcsd
  3. Sep 23, 2012 #2

    mfb

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    Looks like homework.

    With v as initial velocity, can you calculate the horizontal and vertical component of the velocity?
    Based on the vertical component, can you calculate the time until Jim/Bart is at floor level again?
    Based on that time, can you calculate the horizontal position at that point?

    That can be used for both 1 and 2.
     
  4. Sep 23, 2012 #3
    1) Use this
    50 = (v2*sin(2*30))/9.81
    v=23.xx m/sec

    2) Jake doesn't make it. Misses by 9m to 10m. You can use the same formula above but more accurate is
    -1 = (20*sin45)t -4.91*t2
    (-1, because the ramp is 1 m high). Solve for t. Use value of t in
    x = (20*cos45)*t.
    x will be much lower than 50m.

    I think I'm right, but may be not.
     
  5. Sep 24, 2012 #4

    mfb

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    I think you forgot the height of the ramp here.
     
  6. Sep 24, 2012 #5
    Didn't forget, tried a quick-fix. ha ha
    It gives the same answer OP was looking.
    Thanks.
     
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