84.
(a) Using Eq. 11-15 with ω = 0, we have
θ =
ω
0
+ ω
2
t = 2.8 rad .
(b) One ingredient in this calculation is α = (0
−3.5 rad/s)/(1.6 s) = −2.2 rad/s
2
, so that the tangential
acceleration is rα = 0.33 m/s
2
. Another ingredient is ω = ω
0
+ αt = 1.3 rad/s for t = 1.0 s, so that
the radial (centripetal) acceleration is ω
2
r = 0.26 m/s
2
. Thus, the magnitude of the acceleration is
|a| =
0.33
2
+ 0.26
2
= 0.42 m/s
2
.