20. Consider a square of mass 2 kg and side length of lm that is free to rotate

Question

20. Consider a square of mass 2 kg and side length of lm that is free to rotate about a horizontal axis through its corner, as shown in the figure below. What is the gravitational torque about its rotation axis? Hint, use g = 10 m/s^2 axis N m 21. Two people are carrying a 60 kg beam that is 5 m long. The moment of inertia of this beam about one end is I end = 1/3ML^2 = 500 kgm^2. At t=0, right end is released and free to fall. What is the instantaneous angular acceleration of this beam about its left end? Hint, use g = 10 m/s^2 radians/sec^2 22. A flywheel of radius 0.3 m and moment of inertia of 0.5 kgm^2 starts from rest at t=0 and accelerates with an angular acceleration of 2 radians/sec^2. Through what angle does this flywheel rotate in 10 sec? radians

Explanation / Answer

20)

gravitational torque=mg*r

r=distace from axis

but mg act on centre so r=distace of force from axis of rotation=1/2=0.5

gravitational torque=mg*r=2*10*0.5=10

21)

2N=mg=

N=60*g/2=300N

torque=300*5=1500N-m

instanteneous angular accelaration=torque/moment of inertia=1500/500=3rad/sec2

22)

angle=0.5*angular accelaration*t2=0.5*2*102=100rad

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