PHY 2053, Spring 2009, Quiz 8 — Whiting
1. A wheel has a radius of 4.10 m. How far (path length) does a point on the circumference
travel if the wheel is rotated, respectively, through angles of:
a) 30.0◦ ,
∆` = r × ∆θ = 4.10 × 30.0◦ ×
π
= 2.147 m.
180◦
b) 30.0 rad, and
∆` = r × ∆θ = 4.10 × 30.0 = 123.0 m.
c) 30.0 rev.
∆` = r × ∆θ = 4.10 × 30.0 × 2π = 772.8 m.
2. A centrifuge in a medical laboratory rotates at an angular speed of 3600 rev/min. When
switched off, it rotates through 50.0 revolutions before coming to rest.
a) Find the constant angular acceleration of the centrifuge.
Use ω 2 = ω02 + 2α × ∆θ with ω = 0. So:
µ
¶
ω02
2π × 3600 2
1
α=−
=−
×
= −72.0π = −226.2 rad/s2 .
2∆θ
60
2 × 2π × 50.0