/*! 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 17 (I) An automobile engine slows d... [FREE SOLUTION] | 91Ó°ÊÓ

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(I) An automobile engine slows down from 3500 rpm to 1200 rpm in 2.5 s. Calculate \((a)\) its angular acceleration, assumed constant, and \((b)\) the total number of revolutions the engine makes in this time.

Short Answer

Expert verified
Angular acceleration is \(-96.34 \text{ rad/s}^2\) and the engine makes approximately 97.94 revolutions.

Step by step solution

01

Convert Angular Velocities to Radians per Second

First, convert the initial and final angular velocities from revolutions per minute (rpm) to radians per second. Use the conversion factor \(1 \text{ rpm} = \frac{2\pi}{60} \text{ rad/s}\). Initial angular velocity \(\omega_i = 3500 \text{ rpm} \times \frac{2\pi}{60} \approx 366.52 \text{ rad/s}\).Final angular velocity \(\omega_f = 1200 \text{ rpm} \times \frac{2\pi}{60} \approx 125.66 \text{ rad/s}\).
02

Calculate Angular Acceleration

Use the formula for angular acceleration \(\alpha\), which is defined as the change in angular velocity over time:\[ \alpha = \frac{\omega_f - \omega_i}{t} \]Substitute the known values:\[ \alpha = \frac{125.66 - 366.52}{2.5} = -96.344 \text{ rad/s}^2 \]
03

Calculate Total Number of Revolutions

First, use the kinematic equation to find the total angular displacement \(\Delta\theta\), where:\[ \Delta\theta = \omega_i t + \frac{1}{2} \alpha t^2 \]Substitute the values:\[ \Delta\theta = 366.52 \times 2.5 + \frac{1}{2} \times (-96.344) \times (2.5)^2 \]This simplifies to:\[ \Delta\theta = 916.3 - 301.075 = 615.225 \text{ rad} \]Convert radians to revolutions using \(1 \text{ revolution} = 2\pi \text{ rad}\):\[ \text{Revolutions} = \frac{615.225}{2\pi} \approx 97.94 \text{ revolutions} \]

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Key Concepts

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

Angular Displacement
Angular displacement is a measure of how far an object has rotated around a fixed point or axis. It is akin to the distance traveled in linear motion, but instead of linear paths, it applies to rotational movement. This displacement is measured in radians, which are a unit derived from the radius of a circle. One complete revolution around a circle results in an angular displacement of \(2\pi\) radians.

Angular displacement can be found using kinematic equations, especially when the angular acceleration is constant. In our context, once we know the initial angular velocity (\(\omega_i\)), the angular acceleration (\(\alpha\)), and the time (\(t\)) over which the movement occurs, we can use the kinematic formula:
\[\Delta\theta = \omega_i t + \frac{1}{2} \alpha t^2\]
This equation blends the initial rotational movement with the added influence of acceleration over a specified time period. Understanding this relationship helps in determining how much rotation has occurred during a specific time interval.
Angular Velocity
Angular velocity is the rate at which an object rotates around an axis. It defines how quickly the orientation of an object is changing. The unit of angular velocity is typically radians per second (rad/s).

To convert from revolutions per minute (rpm) to rad/s, you can use the conversion factor \(1 \text{ rpm} = \frac{2\pi}{60} \text{ rad/s}\). This conversion is crucial for solving physics problems that involve time and rotational movements. It helps bridge the understanding from standard everyday measurements to fundamental physical units that are used in scientific calculations.
  • Initial angular velocity has a significant impact on the rotation.
  • Final angular velocity represents the speed of rotation at a later time.
  • The change between these two velocities, over time, involves angular acceleration.
Knowing how to switch between these units and understand their physical significance is key in solving problems related to rotational motion.
Kinematic Equations
Kinematic equations provide the foundation for analyzing motion, bridging the gap between linear and angular movements. In the context of rotational motion, they help relate angular displacement, velocity, acceleration, and time. These equations are quite similar to those used for linear motion but adapted for circles and rotation.

One of the essential kinematic equations we use for angular motion is:
\[ \omega_f = \omega_i + \alpha t \]
This equation relates angular velocities and acceleration, indicating how an object’s rotational speed changes over time. Another significant equation is:w
\[ \Delta\theta = \omega_i t + \frac{1}{2} \alpha t^2 \]
which helps us determine the overall rotation, or angular displacement, given a starting angular speed, constant acceleration, and time period.

These equations not only let you calculate precise quantities but also develop a comprehensive understanding of the mechanics involved. They are invaluable tools for solving complex physics problems, where multiple quantities interact and evolve over time in rotational systems.

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Most popular questions from this chapter

(I) Determine the moment of inertia of a 10.8-kg sphere of radius 0.648 m when the axis of rotation is through its center.

A cyclist accelerates from rest at a rate of \(1.00 m/s^2\). How fast will a point at the top of the rim of the tire \((diameter = 68.0 cm)\) be moving after 2.25 s? [\(Hint\): At any moment, the lowest point on the tire is in contact with the ground and is at rest-see Fig. 8-57.

(I) Pilots can be tested for the stresses of flying high-speed jets in a whirling "human centrifuge," which takes 1.0 min to turn through 23 complete revolutions before reaching its final speed. \((a)\) What was its angular acceleration (assumed constant), and \((b)\) what was its final angular speed in rpm?

(II) The tires of a car make 75 revolutions as the car reduces its speed uniformly from 95 km/h to 55 km/h. The tires have a diameter of 0.80 m. \((a)\) What was the angular acceleration of the tires? If the car continues to decelerate at this rate, \((b)\) how much more time is required for it to stop, and \((c)\) how far does it go?

(II) A sphere of radius \(r = 34.5 cm\) and mass \(m = 1.80 kg\) starts from rest and rolls without slipping down a 30.0\(^{\circ}\) incline that is 10.0 m long. \((a)\) Calculate its translational and rotational speeds when it reaches the bottom. \((b)\) What is the ratio of translational to rotational kinetic energy at the bottom? Avoid putting in numbers until the end so you can answer: \((c)\) do your answers in \((a)\) and \((b)\) depend on the radius of the sphere or its mass?

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