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7. Two metal disks, one with radius R1 =0.8 cm and mass M1 = 40kg, and thickness

ID: 2116553 • Letter: 7

Question

7. Two metal disks, one with radius R1 =0.8 cm and mass M1 = 40kg, and thickness 10 cm and the other with radius R2 = 60 cm and mass M2 =35kg and thickness 15 cm, are welded together and mounted on a frictionless axis through their common center. A rope is wound around the inner disk (disk 2). The system is at rest first.

a) What is the inertia of the system about its center? (10 pt)

b) In order to make the disks rotate the rope is pulled with a constant force F = 100 N. What is the torque about the center/axle due to this force? (10 pt)

7. Two metal disks, one with radius R1 =0.8 cm and mass M1 = 40kg, and thickness 10 cm and the other with radius R2 = 60 cm and mass M2 =35kg and thickness 15 cm, are welded together and mounted on a frictionless axis through their common center. A rope is wound around the inner disk (disk 2). The system is at rest first. a) What is the inertia of the system about its center? (10 pt) b) In order to make the disks rotate the rope is pulled with a constant force F = 100 N. What is the torque about the center/axle due to this force? (10 pt)

Explanation / Answer

R1 seems to be 0.8 m rather than 0.8 cm I system =40*0.8^2/2 +35*0.6^2/2 =19.1 kg.m^2 also torque =100*0.6 =60 N.m

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