On a 12.0-cm-diameter audio compact disc (CD), digital bits of information are encoded sequentially along an outward spiraling path. The spiral starts at radius R₁ = 2.5 cm and winds its way out to radius R₂ = 5.8 cm. To read the digital information, a CD player rotates the CD so that the player’s readout laser scans along the spiral’s sequence of bits at a constant linear speed of 1.25 m/s. Thus the player must accurately adjust the rotational frequency ƒ of the CD as the laser moves outward. Determine the values for ƒ (in units of rpm) when the laser is located at R₁ and when it is at R₂.
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Converting Between Linear & Rotational
Problem 52e
Textbook Question
A hammer thrower accelerates the hammer of mass 7.30 kg (Fig. 10–64) from rest within four full turns (revolutions) and releases it at a speed of 26.5 m/s. Assuming a uniform rate of increase in angular velocity and a horizontal circular path of radius 1.20 m, calculate the angle of this force with respect to the radius of the circular motion. (Ignore gravity).

1
Understand the problem: The hammer is undergoing circular motion, and we are tasked with finding the angle of the force with respect to the radius of the circular motion. This involves analyzing the forces acting on the hammer and their components.
Recall that in circular motion, the net force acting on the object is the centripetal force, which points toward the center of the circle. However, the force applied by the thrower has both a tangential component (to increase angular velocity) and a radial component (to maintain circular motion).
The tangential force is responsible for the angular acceleration. Use the relationship between tangential force \( F_t \), mass \( m \), and tangential acceleration \( a_t \): \( F_t = m \cdot a_t \). The tangential acceleration can be found using \( a_t = \frac{\Delta v}{\Delta t} \), where \( \Delta v \) is the change in speed and \( \Delta t \) is the time taken.
The radial force is responsible for keeping the hammer in circular motion. Use the formula for centripetal force: \( F_r = \frac{m \cdot v^2}{r} \), where \( v \) is the final speed and \( r \) is the radius of the circular path.
To find the angle \( \theta \) of the force with respect to the radius, use the relationship \( \tan(\theta) = \frac{F_t}{F_r} \). Calculate \( \theta \) using \( \theta = \arctan\left(\frac{F_t}{F_r}\right) \).

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Angular Velocity
Angular velocity is a measure of how quickly an object rotates around a central point or axis. It is defined as the rate of change of angular displacement and is typically expressed in radians per second. In the context of the hammer throw, the angular velocity increases uniformly as the thrower spins, which is crucial for determining the forces acting on the hammer at the moment of release.
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Centripetal Force
Centripetal force is the net force that acts on an object moving in a circular path, directed towards the center of the circle. It is necessary for maintaining circular motion and is calculated using the formula F_c = m * v^2 / r, where m is mass, v is tangential speed, and r is the radius of the circular path. Understanding this force is essential for analyzing the dynamics of the hammer throw as it relates to the forces acting on the hammer during its circular motion.
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Force Angle in Circular Motion
The angle of force with respect to the radius in circular motion refers to the orientation of the net force acting on an object relative to the radius of its circular path. In the case of the hammer throw, this angle can be determined by analyzing the components of the forces involved, particularly the tangential and centripetal forces. This angle is important for understanding how the force applied by the thrower translates into the hammer's motion and trajectory upon release.
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