A particle, held by a string whose other end is attached to a fixed point C, moves in a circle on a horizontal frictionless surface.If the string is cut, the angular momentum of the particle about the point C:
A)increases
B)decreases
C)does not change
D)changes direction but not magnitude
E)none of these

Question

Quizplus · Accepted Answer

Angular momentum is defined as the cross product of the position vector and linear momentum vector. In this case, since the particle is moving in a circle, the linear momentum vector is always tangent to the circle and perpendicular to the position vector from the center of the circle to the particle. Therefore, the angular momentum vector is pointing in the direction perpendicular to the plane of the circle.

When the string is cut, there is no external torque acting on the particle about point C, since there is no force acting on the particle in the direction perpendicular to its motion. This means that the angular momentum of the particle is conserved about point C, and therefore does not change. Therefore, the correct choice is C, "does not change".

A Particle, Held by a String Whose Other End Is