Tarzan

[tandoorichicken]

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.

[HallsofIvy]

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.