44.
(a) Using Table 11-2(c) and Eq. 11-27, the rotational kinetic energy is
K
=
1
2
Iω
2
=
1
2
1
2
M R
2
ω
2
=
1
4
(500 kg)(200π rad/s)
2
(1.0m)
2
=
4.9
× 10
7
J .
(b) We solve P = K/t (where P is the average power) for the operating time t.
t =
K
P
=
4.9
× 10
7
J
8.0
× 10
3
W
= 6.2
× 10
3
s
which we rewrite as t
≈ 100 min.