Mounted on a low-mass rod of length 0.16 n are four balls (see figure below). Tw

Question

Mounted on a low-mass rod of length 0.16 n are four balls (see figure below). Two balls (shown in red on the diagram), each of mass 0.81 kg, are mounted at opposite ends of the rod. Two other balls, each of rmass 0.26 kg (shown in blue on the diagram), are each mounted a distance 0.04 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 dia perpendicular to the rod, and it takes 0.9 s to make one full rotation. (a) What Iis the moment of inertla of the device about Its center? kg·m" (b) What s the angular speed of the rotating device? rad/s (c) What is the magnitude of the angular momentum of the rotating device? kg ms

Explanation / Answer

(A) moment of point mass about a axis at distance r.

I = m r^2

for given system,

I = 2 (0.81 x (0.16/2)^2) + 2(0.26 x 0.04^2)

I = 0.0112 kg m^2

(B) w = 2pi / T = 2 pi / 0.9 = 6.98 rad/s

(C) L = I w = 0.078 kg m^2 / s

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