Case 1: A DJ starts up her phonograph player. The turntable accelerates uniformly from rest, and takes t1 = 11.6 seconds to get up to its full speed of f1 = 78 revolutions per minute. Case 2: The DJ then changes the speed of the turntable from f1 = 78 to f2 = 120 revolutions per minute. She notices that the turntable rotates exactly n2= 13 times while accelerating uniformly. a. Calculate the angular speed described in Case 1, given as f1 = 78 revolutions per minute, in units of radians/second. b. How many revolutions does the turntable make while accelerating in Case 1? c. Calculate the magnitude of the angular acceleration of the turntable in Case 1, in radians/s^2.
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.
Case 1: A DJ starts up her phonograph player. The turntable accelerates uniformly from rest, and takes t1 = 11.6 seconds to get up to its full speed of f1 = 78 revolutions per minute.
Case 2: The DJ then changes the speed of the turntable from f1 = 78 to f2 = 120 revolutions per minute. She notices that the turntable rotates exactly n2= 13 times while accelerating uniformly.
a. Calculate the angular speed described in Case 1, given as f1 = 78 revolutions per minute, in units of radians/second.
b. How many revolutions does the turntable make while accelerating in Case 1?
c. Calculate the magnitude of the
d. Calculate the magnitude of the angular acceleration of the turntable (in radians/s^2) while increasing to 120 RPM (Case 2).
e. How long (in seconds) does it take for the turntable to go from f1 = 78 to f2 = 120 RPM?
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