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ECP A machine part rotates at an angular speed of \(0.06 \mathrm{rad} / \mathrm{s}\); its speed is then increased to \(2.2 \mathrm{rad} / \mathrm{s}\) at an angular acceleration of \(0.70 \mathrm{rad} / \mathrm{s}^{2}\). (a) Find the angle through which the part rotates before reaching this final speed. (b) In general, if both the initial and final angular speed are doubled at the same angular acceleration, by what factor is the angular displacement changed? Why? Hint: Look at the form of Equation \(7.9 .\)

Short Answer

Expert verified
a) The angular displacement is approximately 2.35 radians. b) The angular displacement is doubled when both the initial and final angular speeds are doubled, given the same angular acceleration.

Step by step solution

01

Calculate the time taken to reach final speed

In the first part of the problem, using the equation \( \omega_f = \omega_i + \alpha t \) where \( \omega_i = 0.06 rad/s,\) \( \omega_f = 2.2 rad/s,\) and \( \alpha = 0.70 rad/s²,\) the time \( t \) can be calculated by rearranging the equation to \( t = (\omega_f - \omega_i) / \alpha \).
02

Calculate the angular displacement

With the time calculated in the previous step, the angular displacement can be found using the equation \( S = \omega_i t + 0.5 \alpha t^2 \). Substituting \( \omega_i = 0.06 rad/s,\) \( \alpha = 0.70 rad/s²,\) and the calculated time from step 1 into the equation will yield the displacement.
03

Analyze the change in angular speed

For the second part of the question, if initial and final speeds (\( \omega_i, \omega_f \)) are doubled, while keeping \( \alpha \) constant, the time to reach final speed from initial remains the same, because in the expression \( t = (\omega_f - \omega_i) / \alpha \), \( \omega_f \) and \( \omega_i \) are doubled, and their difference is also doubled, but this is divided by \( \alpha \) which remains constant.
04

Determine the change in angular displacement

The equation for displacement \( S = \omega_i t + 0.5 \alpha t^2 \) shows that if \( \omega_i \) is doubled, \( S \) is also doubled (since \( t \) remains constant as shown in Step 3), meaning the angular displacement is also doubled. The change in \( S \) is proportional to the change in \( \omega_i \).

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Key Concepts

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

Understanding Angular Speed
Angular speed is a measure of how fast an object rotates or spins around a circle. It is often represented using the Greek letter omega (\( \omega \)). The unit of angular speed is radians per second (rad/s).

If you imagine a wheel spinning, angular speed tells you how many radians it covers per second. In our exercise, a machine part starts with an initial angular speed of \( 0.06 \text{ rad/s} \) and increases to \( 2.2 \text{ rad/s} \).

This change in angular speed gives us an understanding of the initial spinning rate and the final spinning rate of the part after acceleration. The higher the angular speed, the faster the object is rotating.
Exploring Angular Acceleration
Angular acceleration is the rate of change of angular speed. It tells us how quickly an object is speeding up or slowing down its rotation. Represented by the Greek letter alpha (\( \alpha \)), it is measured in radians per second squared (\( \text{rad/s}^2 \)).

For example, in the exercise, the machine part has an angular acceleration of \( 0.70 \text{ rad/s}^2 \). This means that every second, its angular speed increases by \( 0.70 \text{ rad/s} \).

By understanding angular acceleration, you can determine how long it takes for an object to reach a certain speed. This concept is vital for predicting how motion changes over time in rotating systems.
Calculating Angular Displacement
Angular displacement refers to the angle through which an object rotates within a specific time period. Measured in radians, it's represented by the letter \( \theta \). Angular displacement can be calculated from the equation: \[ S = \omega_i t + 0.5 \alpha t^2 \]

In this scenario, you first need to find the time \( t \) it takes for the part to reach its final angular speed using \( \omega_f = \omega_i + \alpha t \). Once you have \( t \), you can calculate \( S \) with the known values of initial angular speed \( \omega_i \) and angular acceleration \( \alpha \), along with the calculated time.

This calculation shows the path traced out by the rotating object, which is crucial for understanding the extent of its motion.
Applying Equations of Motion
Equations of motion in angular kinematics are similar to those in linear motion. They help predict the future position or speed of objects in rotational motion using known variables like initial speed, acceleration, and time.

The equations, such as \( \omega_f = \omega_i + \alpha t \) and \( S = \omega_i t + 0.5 \alpha t^2 \), provide a structured method to solve angular motion problems.

For example, by manipulating these equations in the exercise, we learn that doubling the initial and final angular speeds at a constant acceleration results in doubled angular displacement because the time \( t \) remains constant.

This illustrates how changes in motion parameters affect overall rotation and helps deepen our understanding of rotational dynamics.

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Most popular questions from this chapter

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