A spinning figure skater tucks her arms and legs closer to the axis of rotation

Question

A spinning figure skater tucks her arms and legs closer to the axis of rotation while spinning. Her body rotates much faster in the tucked position than the non-tucked or extended position. This is an example of what physical law? 9) Two gears drive a shaft. The first gear with 40 teeth revolves at 60.0 rpm. The second gear revolves at 80.0 rpm. How many teeth does the second gear have? 10) A pulley of diameter 15.0 cm is driven by a motor and revolves at 100 rpm. The pulley drives a second pulley with diameter 10.0 cm. Find the rpm of the second pulley.

Explanation / Answer

Question 9:

Velocity at the point of contact is same,

r1w1 = r2w2

since module will be same,

z1/z2 = r1/r2 = w2/w1

z2 = z1*w1/w2 = 40*60/80

Number of teeth the second gear have is 30 teeth

Question 10:

D1 = 15cm

N1 = 100 rpm

D2 = 10 cm

N2 = ?

N1*D1 = N2*D2

N2 = 100 *15/10

N2 = 150 rpm

the rpm of the second pulley is 150 rpm.

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