1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I need some serious help

  1. Nov 26, 2004 #1
    Hi I'm AllAmericanGirl2004,

    I need some serious help in my AP Physics class. This last unit, on forces is nearly killing me. Maybe you guys can help me understand this. Here's a problem I'm stuck on...

    Tarzan plans to cross a gorge by swinging in an arc from a hanging vine. If his arms are capable of exerting a force of 1600 N, what is the max speed he can tolerate at the lowest point of his swing? His mass is 80kg and the vine is 6.8 m long.

    Now, it seems to me that the net force is 1600 N and since Tarzan's mass is 80kg, wouldn't you just say that using the F=ma equation that 1600=80a? But that seems way too easy....I don't know. HELP!!!
  2. jcsd
  3. Nov 26, 2004 #2
    Tarzan is moving in an arc...that means that centripetal acceleration is involved...(since he's moving in a circular direction).

    Thusly, there is a centripetal force acting on Tarzan (Fc = mv^2/R) and the graviational force as well (F = mg)....basically...work with that info...and also...try to draw a free body diagram as well.
  4. Nov 26, 2004 #3
    Okay thanks....

    K, so the Fc is the net force right? and what's the R again? R is the length of the vine? But wait, how do you incorparate both equations at once??
  5. Nov 26, 2004 #4
    At the bottom, there are two forces acting on him--his weight and the centripital force. The equation for weight is mg, the equation for centripital force is (mv^2)/r. r is the radius of the circle that the arc is from. m is the mass, and g is gravity. The total force on him at the bottom of the arc would be (mv^2)/r+mg. Since m, g, and r are all constants, the only variable you're working with is v. See what the maximum velocity is that tarazan can handle (his arms can only handle 1600N).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?