1. Igor\'s having some (physics) fun with the Frankenstein monster before he\'s
ID: 1372166 • Letter: 1
Question
1. Igor's having some (physics) fun with the Frankenstein monster before he's been brought (back) to life The monster's legs are dangling over the edge of the table he's laying on and Igor sees that, if displaced, they swing back and forth, pendulum-like, oscillating about the knees. By the hourglass on the shelf, Igor measures the leg-swing period to be 1.50 s. If the mass of Frankie's lower leg is 9.00 kg and its center of mass is 24.0 cm below the knee, what's the lower leg's moment of inertia (about the knee)?Explanation / Answer
Given mass of the leg m = 9 kg
time period is 1.5 s
we know that T = 2*pi sqrt(l/g)
l = T^2 *g / 4*pi^2
= 1.5^2*9.8 / 4*3.14^2
= 0.559 m = 55.9 cm
now moment of inertial of lower leg about knee is
I = (1/3 m L^2) + (m Xcm^2) -------------- paralle axis theorem
= (1/3*9*0.559^2) +(9*0.24^2)
= 1.45584 kg m^2
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