p11_074.pdf

74. The rotational inertia of the passengers is (to a good approximation) given by Eq. 11-26: I = mR 2 =

NmR 2 where N is the number of people and m is the (estimated) mass per person. We apply Eq. 11-44:

W =

2 Iω 2 =

2 NmR 2 ω 2 .

60 = 2160 persons. The rotation rate is constant so that ω = θ/t which

leads to ω =2 π/ 120 = 0 . 052 rad/s. The mass (in kg) of the average person is probably in the range

≤

100, so the work should be in the range

2 (2160)(50)(38) 2 (0 . 052) 2

≤

2 (2160)(100)(38) 2 (0 . 052) 2

10 5 J

≤

10 5 J .

where R =38mand N =36