/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 75 A high-wire walker always attemp... [FREE SOLUTION] | 91Ó°ÊÓ

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A high-wire walker always attempts to keep his center of mass over the wire (or rope). He normally carries a long, heavy pole to help: If he leans, say, to his right (his com moves to the right) and is in danger of rotating around the wire, he moves the pole to his left (its com moves to the left) to slow the rotation and allow himself time to adjust his balance. Assume that the walker has a mass of \(70.0 \mathrm{~kg}\) and a rotational inertia of \(15.0 \mathrm{~kg} \cdot \mathrm{m}^{2}\) about the wire. What is the magnitude of his angular acceleration about the wire if his com is \(5.0 \mathrm{~cm}\) to the right of the wire and (a) he carries no pole and (b) the \(14.0 \mathrm{~kg}\) pole he carries has its com \(10 \mathrm{~cm}\) to the left of the wire?

Short Answer

Expert verified
(a) 2.29 rad/s², (b) 1.37 rad/s².

Step by step solution

01

Calculate net torque without pole

The net torque (\( \tau \)) is given by \( \tau = r \cdot F \), where \( r \) is the distance of the center of mass from the pivot (wire), and \( F \) is the gravitational force. The force due to gravity is \( F = mg \). So, \( \tau_1 = (0.05 \text{ m})(70.0 \text{ kg})(9.8 \text{ m/s}^2) = 34.3 \text{ N}\cdot\text{m} \).
02

Calculate angular acceleration without the pole

Angular acceleration (\( \alpha \)) is given by \( \alpha = \frac{\tau}{I} \), where \( I \) is the rotational inertia.\( \alpha_1 = \frac{34.3 \text{ N}\cdot\text{m}}{15.0 \text{ kg}\cdot\text{m}^2} = 2.29 \text{ rad/s}^2 \).
03

Calculate net torque with the pole

Consider the pole's torque:\( \tau_2 = (0.10 \text{ m})(14.0 \text{ kg})(9.8 \text{ m/s}^2) = 13.72 \text{ N}\cdot\text{m} \). The pole's torque opposes the walker's torque, so\( \tau_{net} = 34.3 \text{ N}\cdot\text{m} - 13.72 \text{ N}\cdot\text{m} = 20.58 \text{ N}\cdot\text{m} \).
04

Calculate angular acceleration with the pole

Again, use \( \alpha = \frac{\tau_{net}}{I} \).\( \alpha_2 = \frac{20.58 \text{ N}\cdot\text{m}}{15.0 \text{ kg}\cdot\text{m}^2} = 1.37 \text{ rad/s}^2 \).

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Key Concepts

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

Understanding Angular Acceleration
Angular acceleration is a measure of how quickly an object's rotational speed changes. It is similar to linear acceleration but applies to rotational motion. In the context of the high-wire walker, angular acceleration controls how swiftly he might start to spin around the wire, making it a crucial aspect of balance.

Angular acceleration (\( \alpha \)) can be calculated using the formula:\[\alpha = \frac{\tau}{I}\]where:
  • \( \tau \) is the net torque, which is the turning force causing the rotation.
  • \( I \) is the rotational inertia, which represents how much the body resists the change in spinning motion.
For the high-wire walker, his angular acceleration is directly influenced by the net torque he experiences and how resistant he is to change due to his distribution of mass (rotational inertia). When balancing, it’s vital that he maintains control over this variable.
Mastering Torque Calculation
Torque can be thought of as a twisting force that leads to rotation around a point, similar to the way a wrench turns a bolt. The size of the torque can greatly influence how quickly something starts to spin.

Calculating torque (\( \tau \)) involves multiplying three key factors:\[\tau = r \cdot F = r \cdot (m \cdot g)\]where:
  • \( r \) is the distance from the pivot point to where the force acts.
  • \( F \) is the force applied, which is often the gravitational force (\( m \cdot g \)).
For the walker, his own weight and its distance from the wire create a torque that might cause him to rotate. When carrying the pole, it adds another opposing torque due to its weight and position, helping to stabilize or destabilize his balance based on its direction of lean.

Understanding how to calculate and manage torque is essential for anyone needing to maintain equilibrium, like the high-wire walker.
Decoding Rotational Inertia
Rotational inertia, also known as the moment of inertia, is a measure of an object's resistance to changes in its rotation. It's akin to the concept of mass in linear motion, dictating how hard it is to start, stop, or alter the spin of an object.

For the high-wire walker without the pole, his rotational inertia solely comes from his body being distributed around the axis of the wire. When he carries the pole, it adds to and influences his overall rotational inertia, distributing mass away from the center even more.

With rotational inertia (\( I \)), larger values mean more resistance to change:
  • Higher \( I \) slows down changes in rotational motion.
  • Lower \( I \) allows quicker adjustments.
In practice, the balance dynamics of the high-wire walker demonstrate how small adjustments and understanding of inertia can make substantial differences in maintaining stability. The calculated value of angular acceleration reflects this critical interplay between torque and rotational inertia.

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Most popular questions from this chapter

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