A disk brake on a car consists of a disk with a 0.121 m radius and a caliper that pushes a frictional surface against the edge of the disk (an idealization of a real brake). The moment of inertia of the disk system is 0.354 kg m2. a)At a certain speed of the car, the angular velocity of the disk is 156 rad/s. If the car manufacture wants the car to go from this speed to a full stop in 17 s, what is the magnitude of the angular acceleration of the disk? b) What is the torque that must be applied to the disk to bring it to rest in this time? c) What is the magnitude of the force that pushes the frictional surface against the disk to slow it to a stop if the coefficient of kinetic friction is 0.424?
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.
A disk brake on a car consists of a disk with a 0.121 m radius and a caliper that pushes a frictional surface against the edge of the disk (an idealization of a real brake). The moment of inertia of the disk system is 0.354 kg m2. a)At a certain speed of the car, the
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