1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Center of mass (vectors)

  1. May 30, 2006 #1
    A big olive (m = 0.11 kg) lies at the origin of an xy coordinate system, and a big Brazil nut (M = 0.82 kg) lies at the point (0.99, 2.1) m. At t = 0, a force Fo = (4i + 4j) N begins to act on the olive, and a force Fn = (-4i -3j) N begins to act on the nut. What is the (a)x and (b)y displacement of the center of mass of the olive-nut system at t = 4.6 s, with respect to its position at t = 0?

    I first started approaching the problem by doing E(sigma)mixi/Emi, and the same for the y-direction. So, for x-direction, it would be:

    (.99molive + 0mnut)/(.82kg + .11kg)

    for the y-direction, it would be:

    (2.1molive + 0mnut)/(.82kg + .11kg)

    I don't even know if I did those correctly.

    For the rest, they give you the force in both directions and the duration time (4.6 sec). I have to find the displaceent, which means I first have to find the center of mass for 0 seconds and then for 4.6 seconds.

    Can someone help me with how to approach this problem, especially how I can use the vector forces? Thank you.
    Last edited: May 30, 2006
  2. jcsd
  3. May 30, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Looks to me like you got the olive and nut mixed up; it's the olive that is at the origin.

    There are two ways to approach this. One way is to treat each "particle" separately: Given the force, find its acceleration, then it's displacement. (Treat each component independently.) Then find the new center of mass at t = 4.6 sec.

    Another way, a bit easier, is to treat the nut and olive as a single system. Find the net force on the system (just add the forces). Then, treating the system as a single "particle" (with mass equal to the total mass of both), you can find the acceleration--and then the displacement--of the center of mass directly.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook