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How would a flywheel's (spinning disk's) kinetic energy change if its moment of inertia were five times larger but its angular speed were five times smaller? A. \(0.1\) times as large as before B. \(0.2\) times as large as before C. same as before D. 5 times as large as before E. 10 times as large as before

Short Answer

Expert verified
C. same as before

Step by step solution

01

Understand the Formula

Remember that the kinetic energy of a spinning disk is given by the formula \( K.E. = \frac{1}{2}Iω^2 \) where \( I \) is the moment of inertia and \( ω \) is the angular speed.
02

Substitute the Given Values

Let's substitute the given values into the kinetic energy equation. If the moment of inertia were five times larger and the angular speed were five times smaller, then the kinetic energy would be given by \( K.E. = \frac{1}{2}*(5I)*(\frac{ω}{5})^2 \)
03

Simplify the Expression

Simplify the above expression: \( K.E. = \frac{1}{2}*5I*\frac{ω^2}{25} = \frac{1}{2}Iω^2 = K.E. \) This is the same as the original kinetic energy.

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Key Concepts

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

Moment of Inertia
The moment of inertia is a concept in physics that helps describe how different objects resist rotational motion, much like how mass describes resistance to linear motion. It's all about how mass is distributed relative to an axis of rotation. The further away the mass is from the axis, the larger the moment of inertia.

Think of it like this: when you're spinning a bicycle wheel, it feels different to spin it from the tire (far from the hub) versus spinning it from the hub (close in). The tire's heavier distribution gives it a larger moment of inertia.
  • Increases when mass is farther from the axis.
  • Affects how easily an object rotates.
  • Critical for understanding rotational motion in mechanics.
In the exercise, by increasing the moment of inertia by five times, we're essentially making it harder for the flywheel to start spinning. But when we also reduce angular speed by five times, it's a balancing act.
Angular Speed
Angular speed tells us how fast something spins or rotates. It is the rate at which the angle changes during rotation, often measured in radians per second. The faster something spins, the greater its angular speed.

Imagine you're on a merry-go-round. If it spins quickly, you make a complete circle faster, indicating a high angular speed. Conversely, a slow spin means a small angular speed.
  • Measures the rate of rotation.
  • Impacts how quickly an object travels along a circular path.
  • A key factor in calculating rotational kinetic energy.
In the problem, reducing the angular speed by five times seems like a drastic change. However, when calculating kinetic energy, this decrease compensates for the increase in the moment of inertia, leading to the conclusion that the kinetic energy remains unchanged.
Physics Education
Physics education is about making complex concepts simple and understandable. It's crucial for students to grasp abstracts like moment of inertia and angular speed because they form the foundation of mechanics.

A good physics education uses real-world examples, simplifies equations to their core elements, and encourages hands-on experimentation. Consider the flywheel problem: it combines these concepts in a practical way.
  • Breaks down complex scientific principles.
  • Uses real-life scenarios for better understanding.
  • Encourages problem-solving and critical thinking skills.
When teaching about kinetic energy in rotational systems, it's helpful to visualize or even experiment with rotational objects, fostering deeper comprehension. By working through problems step-by-step, like the exercise provided, students gain confidence and proficiency in physics.

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Most popular questions from this chapter

The moment of inertia of a thin ring about its symmetry axis is \(I_{\mathrm{CM}}=M R^{2}\). What is the moment of inertia if you twirl a large ring around your finger, so that in essence it rotates about a point on the ring, about an axis parallel to the symmetry axis? A. \(5 M R^{2}\) B. \(2 M R^{2}\) C. \(M R^{2}\) D. \(1.5 M R^{2}\) E. \(0.5 M R^{2} \mathrm{SSM}\)

What is the angular momentum of a \(70-\mathrm{kg}\) person riding on a Ferris wheel that has a diameter of \(35 \mathrm{~m}\) and rotates once every \(25 \mathrm{~s}\) ? SSM

Medical When the palmaris longus muscle in the forearm is flexed, the wrist moves back and forth (Figure \(8-64)\). If the muscle generates a force of \(45 \mathrm{~N}\) and it is acting with an effective lever arm of \(22 \mathrm{~cm}\), what is the torque that the muscle produces on the wrist? Curiously, over \(15 \%\) of all Caucasians lack this muscle; a smaller percentage of Asians (around 5\%) lack it. Some studies correlate the absence of the muscle with carpal tunnel syndrome.

In your own words, describe the quantity \(d m\) that is found in the integral equation for moment of inertia: $$ I=\int r^{2} d m \operatorname{SSM} $$

Analyze the following statement and determine if there are any physical inconsistencies: While rotating a ball on the end of a string of length \(L\), the rotational kinetic energy remains constant as long as the length and angular speed are fixed. When the ball is pulled inward and the length of the string is shortened, the rotational kinetic energy will remain constant due to conservation of energy, but the angular momentum will not, because there is an external force acting on the ball to pull it inward. The moment of inertia and angular speed will, of course, remain the same throughout the process because the ball is rotating in the same plane throughout the motion.

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