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!

Centripetal motion problem

  1. Nov 2, 2005 #1
    "A mass of 3.900 kg is suspended from a 1.450 m long string. It revolves in a horizontal circle.
    The tangential speed of the mass is 3.247 m/s. Calculate the angle between the string and the vertical (in degrees)."

    Here is a diagram, labelling angle theta I'm supposed to solve for: http://capaserv.physics.mun.ca/msuphysicslib/Graphics/Gtype11/prob03_pendulum.gif

    I've deduced so far that: sin(theta) = opp/hyp

    In this case, opp = radius and hyp = length of string (L) or (1.450 m)

    So sin(theta) = r/L

    In turn, r can be solved by means of Fc = mv^2/r, as r = mv^2/Fc

    so sin(theta) = mv^2/FcL

    M is given, V is given, and L is given. Fc I'm sort of puzzled on, since I can't use the MV^2/R equation again. Any clues?
     
  2. jcsd
  3. Nov 2, 2005 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: What provides the centripetal force?
    Hint: Consider both vertical and horizontal forces acting on the mass.
     
  4. Nov 2, 2005 #3
    Okay, I think I'm getting somewhere. Would it be right to say the Fc is equal to the x-factor of the weight of the mass on the string? I could say this therefore:

    Fc = mgsin(theta)

    and then

    sin(theta) = mv^2/mgsin(theta)L

    which would cancel mass, giving me:

    sin(theta) = v^2/gsin(theta)L

    would that be right? or is mass even significant in this problem?
     
  5. Nov 3, 2005 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Not right. For one thing, the weight of the mass acts down--it has no horizontal component.

    Try this: Identify all the forces acting on the mass. (There are two forces.) Then consider horizontal and vertical components.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Centripetal motion problem
Loading...