   Chapter 7, Problem 10P

Chapter
Section
Textbook Problem

The tub of a washer goes into its spin-dry cycle, starting from rest and reaching an angular speed of 5.0 rev/s in 8.0 s. At this point, the person doing the laundry opens the lid, and a safety switch turns off the washer. The tub slows to rest in 12.0 s. Through how many revolutions does the tub turn during the entire 20-s interval? Assume constant angular acceleration while it is starting and stopping.

To determine
The total number of revolutions the tub undergo in the entire accelerating and decelerating process.

Explanation

Given info: The tub accelerates from rest to 5.0revs-1 in a time interval of 8.0s . Then the tub decelerates to rest in 12.0s . The angular acceleration in the entire process is constant.

Explanation:

The angular displacement in an interval is defined as,

Δθ=(ωf+ωi2)t

• ωf is the final angular velocity in the interval
• ωi is the initial angular velocity in the interval
• t is the time interval

For the accelerating interval, substitute 5.0revs-1 for ωf , 0 for ωi and 8.0s for t to determine the angular displacement,

For the decelerating interval, substitute 0 for ωf , 5

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