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Tarzan in trouble - Kinematics

  1. Nov 23, 2003 #1
    Tarzan is in trouble once again and Jane and Cheetah have to decide whether to try to bail him out. Jane and Cheetah (70kg combined) are perched on a cliff 10m above Tarzan (70kg) and can swing down on a vine and grab him. To get to safety, they need to get to a perch 5m above Tarzan on the other side.

    Determine the speed of Jane and Cheetah just before they would grab Tarzan. Assume no air drag or friction.
  2. jcsd
  3. Nov 23, 2003 #2


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    That should be fairly straight forward if you use "conservation of energy". Take Tarzan's position as 0 potential energy. Since they need to get to a position 5 m above Tarzan, where the potential energy of all 3 is 140g(5)= 700(9.81)= 6867 Joules, their total energy must be greater than 6867 Joules.
    You know that the combined mass of Cheetah and Jane is 70 kg. so, taking V as their speed (in m/s) just before they "pickup" Tarzan, their kinetic energy is 35V2 Joules. Since their potential energy is now 0, their total energy is 35V2.

    Solve 35V2= 6867.
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