## A pencil sharpener takes 1.4 seconds to go from its maximum speed of 8π rad/s to rest.

**A pencil sharpener takes 1.4 seconds to go from its maximum speed of 8π rad/s to rest. How many rotations will the pencil sharpener make before it stops?**

**Starting from rest. A DVD takes 0.2 seconds to get its maximum rotational velocity of 14π r radiant per second. What is the angular acceleration of the DVD?**

**Jordan is in a casino waiting for her number to be called at the roulette wheel, a large 3.0-kg disk of radius 0.60 m. What is rotational inertia of the wheel?**

## Answer ( 1 )

1) α = w/t = 8π/1.4 = 5.7143π rad/sec² → Θ = w²/(2α) = 17.6 rad = 2.8 revolutions

2) α = dw/dt = 14π/0.2 = 219.9 rad/sec²

3) I = ½mR² = .54 kg∙m² → Rotational inertia L = 0.54*w where w is the angular velocity of the wheel.