物理科題目Rotation求解?

1. Distance of the point of interest from the axis of rotation of the earth
= 6309.cos(39.7) km = 4854 km

Since the earth rotates 1 complete revolution (i.e. 2.pi radians) in 24 hours,
angular velocity of earth rotation = 2.pi/24 radians/hr = pi/12 rad/hr

Because every point on earth surface has the same angular velocity, hence,
linear speed of the point = radius of rotation x angular velocity
= 4854 x pi/12 km/hr = 1271 km/hr

(b) Angular velocity of the forearm = 28.4/0.5 rad/s = 56.8 rad/s
Hence, kinetic energy of the rotating forearm
= (1/2).(0.73).(56.8)^2 J
= 1178 J