1. At the local swimming hole, a favorite trick is to run horizontally off a cli

Question

1. At the local swimming hole, a favorite trick is to run horizontally off a cliff that is 6.5 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 1.2 rev/s. Ignore air resistance and determine the number of revolutions she makes while on the way down. ? rev

2. A string trimmer is a tool for cutting grass and weeds; it utilizes a length of nylon "string" that rotates about an axis perpendicular to one end of the string. The string rotates at an angular speed of 43 rev/s, and its tip has a tangential speed of 57 m/s. What is the length of the rotating string? ? m

Explanation / Answer

1) 6.5 m is the height from which the diver drops,

the time it takes to reach the water is : 1.14 seconds ( using s = 0.5*a*t2)

so number of revolutions is : 1.14*1.2 = 1.37 revolutions

2) 43 revolutions/second is 43*2*pie revolutions/second = 270.18 rad/sec

veloctiy = angular speed*length

57 = 270.18*x

x = 21.1 cm

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