(d) The figure below represents the stick at its lowest position. On this figure, draw a vector to
represent the net force on the rod’s center of mass at this point. Justify your answer.Solutions to Practice Problems
1 . A— The farther the mass from the midpoint, the larger its contribution to the rotational inertia. In
choice A the mass is as far as possible from the midpoint; because all items have the same mass, A
must have the largest I .
2 . C— The angular momentum of a point particle moving in a straight line about a position near the
particle is mvr , where r is the distance of closest approach. This value is constant as long as the
particle keeps going in a straight line, which our pool ball does.
3 . D— Torque is force times the distance to the fulcrum. The force in question is FN , and acts straight
up at the base of the ladder. The distance used is the distance perpendicular to the normal force; this
must be (L /2) cos θ , as shown below:4 . D— The angular position function is given by the integral of the angular velocity function with respect
to time. The limits on the integral are 2 and 3 seconds: