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Review Multiple-Concept Example 7 in this chapter as an aid in solving this problem. In a fast-pitch softball game the pitcher is impressive to watch, as she delivers a pitch by rapidly whirling her arm around so that the ball in her hand moves on a circle. In one instance, the radius of the circle is \(0.670 \mathrm{m} .\) At one point on this circle, the ball has an angular acceleration of \(64.0 \mathrm{rad} / \mathrm{s}^{2}\) and an angular speed of \(16.0 \mathrm{rad} / \mathrm{s} .\) (a) Find the magnitude of the total acceleration (centripetal plus tangential) of the ball. (b) Determine the angle of the total acceleration relative to the radial direction.

Short Answer

Expert verified
(a) Total acceleration is approximately 176.73 m/s². (b) The angle is about 14.04°.

Step by step solution

01

Identify Known Values

We are given the following values:- Radius of the circle, \( r = 0.670 \text{ m} \)- Angular acceleration, \( \alpha = 64.0 \text{ rad/s}^2 \)- Angular speed, \( \omega = 16.0 \text{ rad/s} \)
02

Calculate Tangential Acceleration

The tangential acceleration \( a_t \) can be calculated using the formula:\[ a_t = r \alpha \]Substitute the known values:\[ a_t = 0.670 \times 64.0 = 42.88 \text{ m/s}^2 \]
03

Calculate Centripetal Acceleration

The centripetal acceleration \( a_c \) is calculated using the formula:\[ a_c = r \omega^2 \]Substitute the given values:\[ a_c = 0.670 \times (16.0)^2 = 171.52 \text{ m/s}^2 \]
04

Calculate Total Acceleration

The total acceleration \( a \) is the vector sum of the tangential acceleration \( a_t \) and the centripetal acceleration \( a_c \). Thus, it can be found using:\[ a = \sqrt{a_t^2 + a_c^2} \]\[ a = \sqrt{(42.88)^2 + (171.52)^2} \]\[ a = \sqrt{1838.94 + 29419.42} \]\[ a = \sqrt{31258.36} \approx 176.73 \text{ m/s}^2 \]
05

Determine the Angle of Total Acceleration

The angle \( \theta \) relative to the radial direction can be calculated using:\[ \tan \theta = \frac{a_t}{a_c} \]\[ \tan \theta = \frac{42.88}{171.52} \approx 0.25 \]\[ \theta = \tan^{-1}(0.25) \approx 14.04^\circ \]

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Key Concepts

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

Angular Acceleration
Angular acceleration is a measure of how quickly an object is rotating faster or slower. Simply put, it's the rate of change of angular velocity. The unit is radians per second squared (rad/s²). It plays a vital role in rotational motion as it tells us how quickly an object like a softball in a pitch can speed up or slow down its rotation.
Formula: Understanding How Angular Acceleration Works
Angular acceleration (\( \alpha \) ) is calculated using the formula:
  • \( \alpha = \frac{\Delta \omega}{\Delta t} \)
taking the change in angular speed (\( \Delta \omega \) ) over time (\( \Delta t \) ). This information helps us understand how abrupt or gradual the change in rotation is.
But in our original example, we already have a given angular acceleration (\( \alpha = 64.0 \, \text{rad/s}^2 \) ), which indicates a rapid increase in the pitch's speed. This acceleration is crucial for calculating other components like tangential acceleration, which further explains how the velocity in `rotation` terms translates into linear motion.
Centripetal Acceleration
Centripetal acceleration is the acceleration towards the center of a circular path. It's necessary to maintain an object moving along a circular pathway. In terms of our pitching softball, this acceleration is what keeps the ball moving in a circle.
Formula: Calculating Centripetal Acceleration
To calculate centripetal acceleration (\( a_c \) ) we use:
  • \( a_c = r \omega^2 \)
where \( r \) is the radius (0.670 m in our scenario) and \( \omega \) is the angular speed (16.0 rad/s). For this situation, substituting the values into the formula, we find \( a_c = 171.52 \, \text{m/s}^2 \) .
This powerful force ensures that even as the ball increases in speed due to angular acceleration, it continues to follow its intended circular path. Without centripetal acceleration, the ball would aimlessly drift off its circle!
Tangential Acceleration
Tangential acceleration is what it sounds like: the acceleration directed along the edge, or tangent, of the circle. It highlights how the object gains or loses speed as it rotates.
Understanding the Formula for Tangential Acceleration
To derive tangential acceleration (\( a_t \) ), the equation used is:
  • \( a_t = r \alpha \)
where \( r \) is the radius, and \( \alpha \) is the angular acceleration. Using the provided values, \( a_t = 42.88 \, \text{m/s}^2 \) for our example, shows how fast the ball picks up speed in the direction it is already spinning.
Simply put, tangential acceleration tells us the change in speed of the ball as it travels around the circle. This component, combined with centripetal acceleration, helps calculate the total acceleration of the ball in the game.

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Most popular questions from this chapter

A stroboscope is a light that flashes on and off at a constant rate. It can be used to illuminate a rotating object, and if the flashing rate is adjusted properly, the object can be made to appear stationary. (a) What is the shortest time between flashes of light that will make a three-bladed propeller appear stationary when it is rotating with an angular speed of \(16.7 \mathrm{rev} / \mathrm{s} ?\) (b) What is the next shortest time?

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At the local swimming hole, a favorite trick is to run horizontally off a cliff that is \(8.3 \mathrm{m}\) above the water. One diver runs off the edge of the cliff, tucks into a "ball," and rotates on the way down with an average angular speed of 1.6 rev/s. Ignore air resistance and determine the number of revolutions she makes while on the way down.

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