On an old-fashioned rotating piano stool, a woman sits holding a pair of dumbbells at a distance of 0.580 mm from the axis of rotation of the stool. She is given an angular velocity of 3.45 rad/srad/s , after which she pulls the dumbbells in until they are only 0.150 mm distant from the axis. The woman's moment of inertia about the axis of rotation is 4.65 kg⋅m2kg⋅m2 and may be considered constant. Each dumbbell has a mass of 5.45 kgkg and may be considered a point mass. Neglect friction. What is the initial angular momentum of the system? What is the angular velocity of the system after the dumbbells are pulled in toward the axis?
Angular Momentum
The momentum of an object is given by multiplying its mass and velocity. Momentum is a property of any object that moves with mass. The only difference between angular momentum and linear momentum is that angular momentum deals with moving or spinning objects. A moving particle's linear momentum can be thought of as a measure of its linear motion. The force is proportional to the rate of change of linear momentum. Angular momentum is always directly proportional to mass. In rotational motion, the concept of angular momentum is often used. Since it is a conserved quantity—the total angular momentum of a closed system remains constant—it is a significant quantity in physics. To understand the concept of angular momentum first we need to understand a rigid body and its movement, a position vector that is used to specify the position of particles in space. A rigid body possesses motion it may be linear or rotational. Rotational motion plays important role in angular momentum.
Moment of a Force
The idea of moments is an important concept in physics. It arises from the fact that distance often plays an important part in the interaction of, or in determining the impact of forces on bodies. Moments are often described by their order [first, second, or higher order] based on the power to which the distance has to be raised to understand the phenomenon. Of particular note are the second-order moment of mass (Moment of Inertia) and moments of force.
On an old-fashioned rotating piano stool, a woman sits holding a pair of dumbbells at a distance of 0.580 mm from the axis of rotation of the stool. She is given an
What is the initial
What is the angular velocity of the system after the dumbbells are pulled in toward the axis?
Compute the kinetic energy of the system before the dumbbells are pulled in.
Compute the kinetic energy of the system after the dumbbells are pulled in.
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