p11_025.pdf

25. (a) In the time light takes to go from the wheel to the mirror and back again, the wheel turns through

an angle of θ =2 π/ 500 = 1 . 26

10 − 2 rad. That time is

t = 2

2(500 m)

2 . 998

10 8 m / s =3 . 34 × 10 − 6 s

so the angular velocity of the wheel is

t = 1 . 26

10 − 2 rad

=3 . 8

10 3 rad / s .

3 . 34

10 − 6 s

(b) If r is the radius of the wheel, the linear speed of a point on its rim is

v = ωr = 3 . 8

10 3 rad / s (0 . 05 m) = 190 m / s .

ω = θ