An automatic dryer spins wet clothes at an angular speed of 5.4 rad/s. Starting

Question

An automatic dryer spins wet clothes at an angular speed of 5.4 rad/s. Starting from rest, the dryer reaches its operating speed with an average angular acceleration of 4.0 rad/s2. How long does it take the dryer to come up to speed?

At the local swimming hole, a favorite trick is to run horizontally off a cliff that is 5.17 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 2.26 rev/s. Ignore air resistance and determine the number of revolutions she makes while on the way down.

Explanation / Answer

Use kinematic equation,

wf=wi+*t

5.4=0+4.0*t

t=5.4/4.0 = 1.35s

Let us first calculate the total time required for diver for the way down,

h=vi*t-1/2*gt^2

-5.17=0*t -1/2*9.8*t^2

t=1.027s

No of rev = angular velocity*time = 2.26*1.027 = 2.32 rev

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