Four balls are securely mounted to a rod of length 0.36 m which we will assume h

Question

Four balls are securely mounted to a rod of length 0.36 m which we will assume has no mass. The two red balls, each of mass 0.86 kg, are mounted at opposite ends of the rod. The two blue balls, each of mass 0.35 kg, are each mounted a distance 0.09 m from the center of the rod. The rod rotates on an axle through the center of the rod (indicated by the "x" in the diagram), perpendicular to the rod, and it takes 1.4 seconds to make one full rotation. (a) What is the rotational inertia of the device about its center? I = kg middot m^2 (b) What is the angular speed of the rotating device? omega = radians/s (c) What is the magnitude of the angular momentum of the rotating device? |L| = kg middot m^2/s

Explanation / Answer

m1 =0.86 kg, r1= 0.18 m , m2 =0.35 kg, r2 =0.09

T =1.4 s

(a) I = 2*m1r1^2 +2*m2r2^2

I = (2*0.86*0.18^2)+(2*0.35*0.09^2)

I =0.0614 kg.m^2

(b) w = 2pi/T = 2*3.14/1.4 = 4.486 rad/s

(c) L = Iw = 0.0614*4.486

L = 0.275 kg.m^2/s

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