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An athlete swings a \(5.00-\mathrm{kg}\) ball horizontally on the end of a rope. The ball moves in a circle of radius \(0.800 \mathrm{~m}\) at an angular speed of \(0.500 \mathrm{rev} / \mathrm{s}\). What are (a) the tangential speed of the ball and (b) its centripetal acceleration? (c) If the maximum tension the rope can withstand before breaking is \(100 \mathrm{~N}\), what is the maximum tangential speed the ball can have?

Short Answer

Expert verified
The tangential speed of the ball is \(2.5 \, m/s\), its centripetal acceleration is \(7.8 \, m/s^{2}\), and the maximum tangential speed the ball can have without breaking the rope is \(4 \, m/s\).

Step by step solution

01

Convert Angular Speed

Firstly, convert the angular speed from revolutions per second (rev/s) to radian per second (rad/s) by multiplying by \(2\pi\) (since one revolution is \(2\pi\) radian). So, \(\omega = 0.500 \times 2\pi = 1\pi\) rad/s.
02

Calculate Tangential Speed

The tangential speed \(v\) can be calculated using the formula \(v = \omega r\), where \(\omega\) is the angular speed and \(r\) is the radius. Substituting the given values, we get: \(v = 1\pi \times 0.800 = 2.5\) m/s.
03

Calculate Centripetal Acceleration

The centripetal acceleration \(a_c\) can be calculated using the formula \(a_c = v^2 / r\), where \(v\) is the tangential speed and \(r\) is the radius. Substituting the calculated \(v\) and given \(r\), we get: \(a_c = (2.5)^2 / 0.800 = 7.8 \, m/s^{2}\).
04

Determine Maximum Tangential Speed

The maximum tangential speed \(v_{max}\) can be calculated using the formula \(T = mv_{max}^2 / r\), where \(T\) is the tension, \(m\) is the mass, and \(r\) is the radius. Rearranging for \(v_{max}\) and substituting the given values, we get: \(v_{max} = \sqrt{(T \times r) / m} = \sqrt{(100 \times 0.800) / 5.00} = 4\) m/s.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Angular Speed
The concept of angular speed is pivotal when analyzing objects moving in a circular path. It refers to how fast an object rotates or revolves relative to another point, typically the center of a circle. In physics, angular speed (\f \( \omega \)) is measured in radians per second (rad/s). One revolution equals \(2\pi\) radians, which is the basis for converting from revolutions per second to radian per second, a common requirement in circular motion problems.

For instance, if an object makes half a revolution per second (\f0.500 rev/s\fg), as in our exercise, its angular speed is \f \(0.500 \times 2\pi\) rad/s\fg, which simplifies to \f \(1\pi\) rad/s\fg. Understanding angular speed allows us to predict the behavior of objects in rotation and relates directly to tangential speed, which is the speed at which the object moves along the circular path.
Tangential Speed
Tangential speed, or linear speed, is the rate at which an object moves along the circumference of a circle. Interestingly, it is directly proportional to both the radius of the circle and the angular speed of the object. The formula to calculate tangential speed (\(v\)) is \(v = \omega r\), where \(\omega\) is the angular speed and \(r\) is the radius of the circular path.

In the context of our exercise, with a radius (\(r\)) of 0.800 m and an angular speed (\(\omega\)) of \(1\pi\) rad/s, we calculate the tangential speed to be \(v = 1\pi \times 0.800 = 2.5\) m/s. This speed is crucial as it represents the actual velocity at which the athlete's ball is traveling in its circular path and is used to determine other dynamics of circular motion such as centripetal acceleration.
Maximum Tension
Tension is the force that is transmitted through a rope, cable, or any string-like object when it is pulled tight by forces acting from opposite ends. In circular motion, the maximum tension is the largest force the rope can handle before breaking. This is critical for objects in rotation as it influences the maximum tangential speed they can achieve without breaking the rope. The formula for tension (\(T\)) in a circular motion is derived from the centripetal force and is given by \(T = m v_{max}^{2} / r\).

Revisiting the athlete's scenario, we find that the maximum tension the rope can withstand is 100 N. Using this information, along with the mass of the ball and the radius of the circular path, we can find the maximum tangential speed the ball can have before the rope breaks, ensuring the athlete's safety during the exercise. The calculated maximum tangential speed gives us a boundary within which the ball can move safely.
Physics of Circular Motion
Physics of circular motion encompasses the movement of objects along a circular path and involves concepts of angular speed, tangential speed, centripetal acceleration, and other forces, such as tension. Centripetal acceleration, for instance, is the acceleration that keeps an object moving in a circular path and is directed towards the center of the circle. The equations of motion in the case of a circular trajectory are special because they must account for the fact that direction changes continuously, even if the speed remains constant.

Understanding circular motion's principles and how they interrelate is essential for solving physics problems in this area. The questions regarding the athlete's ball demonstrate the application of these principles, where we analyze the motions and forces to ensure the motion remains stable and within the material constraints of the rope. Exploration of these concepts deepens comprehension of how objects behave under the influence of centripetal forces, laying the groundwork for more advanced studies, such as planetary motion and the movement of electrons in atoms.

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Most popular questions from this chapter

In Robert Heinlein's The Moon Is a Harsh Mistress, the colonial inhabitants of the Moon threaten to launch rocks down onto Earth if they are not given independence (or at least representation). Assuming a gun could launch a rock of mass \(m\) at twice the lunar escape speed, calculate the speed of the rock as it enters Earth's atmosphere.

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A potter's wheel moves uniformly from rest to an angular speed of \(1.00 \mathrm{rev} / \mathrm{s}\) in \(30.0 \mathrm{~s}\). (a) Find its angular acceleration in radians per second per second. (b) Would doubling the angular acceleration during the given period have doubled final angular speed?

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