Torque net

  1. A 4 kg mass is connected by a light cord to a 3 kg mass on a smooth surface.The cord is around a frictionless axle and has a moment of inertia of .5 kg*m^2 and a radius of .3m. Assuming that the cord does not slip arount the axle,

    a) what is the acceleration of the two masses

    b)what are the forces of tension in the rope that connects to the two masses

    I began this problem using the principle that if, as the first question shows, there is acceleration, then torque net is not equal to zero. In such a situation, the following equation is recommended:

    moment of inertia* angular acceleration= sum of the torques. The equation for torque is force*distance from axis.

    Apparently in such a problem, the torque net equation above must be supplemented with force net equations for each of the two masses. The force net equation is:

    Force net *linear acceleration= sum of forces

    By substituting the unknowns in the force net equation into the torque net equation, one should be able to find the acceleration and then the two forces.
  2. jcsd
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