/*! 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 8 A uniform \(1.4-\mathrm{kg}\) ro... [FREE SOLUTION] | 91Ó°ÊÓ

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A uniform \(1.4-\mathrm{kg}\) rod that is 0.75 \(\mathrm{m}\) long is suspended at rest from the ceiling by two springs, one at each end of the rod. Both springs hang straight down from the ceiling. The springs have identical lengths when they are unstretched. Their spring constants are 59 \(\mathrm{N} / \mathrm{m}\) and 33 \(\mathrm{N} / \mathrm{m}\) . Find the angle that the rod makes with the horizontal.

Short Answer

Expert verified
The rod makes an angle of approximately 2.15 degrees with the horizontal.

Step by step solution

01

Understanding the Problem

We have a rod of mass 1.4 kg and length 0.75 m suspended by two springs. The goal is to find the angle the rod makes with the horizontal. One spring has a constant of 59 N/m, and the other has a constant of 33 N/m. Both springs are initially unstretched.
02

Setting Up Forces and Torques

The forces involved include the weight of the rod and the forces from the two springs. Since the rod is in static equilibrium, the sum of forces and torques must be zero. The rod's weight acts downward at its center. The springs will be pulled down by unequal lengths due to their different spring constants, which causes torque.
03

Express the Spring Forces

Let the extensions of the springs be denoted as \(x_1\) and \(x_2\). Using Hooke's Law, the forces exerted by the springs are \(F_1 = k_1 x_1\) and \(F_2 = k_2 x_2\). For static equilibrium, the sum of vertical forces must be equal to the gravitational force acting on the rod: \(F_1 + F_2 = Mg\).
04

Determine Torque Balance

Assume one spring is extended by more than the other. Therefore, a torque will arise, causing the rod to tilt. Taking moments about the center of the rod gives us: \(F_1 (L/2)( ext{cos} \theta) - F_2 (L/2)( ext{cos} \theta) = 0\). However, since the rod is at rest, the net torque due to spring forces should be zero.
05

Solving for x1 and x2

From Step 3, using the force equilibrium equation \(x_1 = \frac{Mg}{k_1 + k_2}\). Then determine \(x_2\) given \(x_1\) and using equilibrium torque: \(x_2 = x_1\left(\frac{k_1}{k_2}\right)\).
06

Calculating the Angle

Using the known spring extensions, calculate the angle \( \theta \) by using the small angle approximation in equilibrium conditions: \(\text{tan} \theta = \frac{x_1 - x_2}{L}\). In this specific scenario, since \(x_1 > x_2\), the rod tilts slightly, and we use inverse tangent to find an approximate angle.

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Key Concepts

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

Spring Constant
The spring constant is a crucial factor in understanding how springs behave when subjected to a force. It is denoted by the symbol \( k \) and represents the stiffness of a spring. A higher spring constant means a stiffer spring, while a lower spring constant indicates a more flexible one. Springs with high spring constants require more force to elongate or compress them by the same amount compared to springs with lower constants.

For example, in our exercise, two springs with constants 59 N/m and 33 N/m are used to suspend a rod. This difference in spring constants means they will stretch by different amounts when the same mass is applied. This uneven stretching is key in understanding how the angle of the rod with the horizontal is created. The difference is essential to calculate the extensions of each spring, which ultimately affects the overall balance and orientation of the system.
Torque
Torque is a measure of the rotational force applied to an object. It is calculated by the product of the force applied and the distance from the pivot point, where the force causes rotation. The basic formula for torque \( \tau \) is \( \tau = r \cdot F \cdot \sin(\theta) \), where \( r \) is the distance to the pivot, \( F \) is the force applied, and \( \theta \) is the angle between the force and the lever arm.

In the scenario with the suspended rod, torque is created by the force difference exerted by the two springs. Since the spring constants are unequal, each spring extends differently, causing a torque about the rod's center. Torque in this case tries to rotate the rod around its center of mass until equilibrium is reached, balancing the different stretching of each spring and the gravitational pull on the rod itself. Understanding the role of torque is vital to decipher the angle the rod makes with the horizontal.
Hooke's Law
Hooke's Law describes how springs respond to external forces. It states that the force \( F \) exerted by a spring is proportional to its displacement \( x \), or \( F = kx \). This linear relationship holds as long as the elastic limit of the spring is not exceeded.

In our exercise, Hooke's Law helps us express the forces from the springs as \( F_1 = k_1 x_1 \) and \( F_2 = k_2 x_2 \). By knowing the spring constants \( k_1 \) and \( k_2 \), and considering the equilibrium condition, we can calculate the extension \( x_1 \) and \( x_2 \). These calculations are pivotal for finding the spring force contributions to both the net force and the torque, ensuring the rod remains in equilibrium.
  • The relationship is linear: force increases consistently with extension.
  • Applies within the spring's elastic limits, ensuring no permanent deformation.
Angle of Inclination
The angle of inclination is the angle that a structure, like a suspended rod, makes with the horizontal. It's a vital component when analyzing systems in static equilibrium.

In this scenario, the combined effect of gravity and the unequal spring constants causes the rod to tilt. By calculating the difference in spring extensions using the equilibrium conditions, we use the small angle approximation to estimate the inclination of the rod. The formula, \( \text{tan} \theta = \frac{x_1 - x_2}{L} \), allows us to find \( \theta \).
  • In cases of slight angles, \( \theta \) can be approximated using \( \text{tan}^{-1} \) (inverse tangent function).
  • Smaller angles imply a closer alignment to the horizontal.
  • Understanding this concept is crucial when balancing forces and torques in mechanical systems.
This concept is essential for ensuring that the rod maintains its equilibrium position and for predicting the system's response to various forces.

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