A combination lock has a 1.1-cm-diameter knob that is part of the dial you turn

Question

A combination lock has a 1.1-cm-diameter knob that is part of the dial you turn to unlock the lock. To turn that knob, you grip it between your thumb and forefinger with a force of 5.0N as you twist your wrist. Suppose the coefficient of static friction between the knob and your fingers is  0.75.

Part A

What is the most torque you can exert on the knob without having it slip between your fingers? I found the torque to be 4.1 X 10-2 N * meters.

Part B

If the maximum torque causes the knob to rotate at 15RPM after 30s of being constantly applied, what is the knob's moment of inertia I ?

Explanation / Answer

I have solved this question earlier with different figures. Please workout using yours figures. If you need any further help just PM me. If I have helped you please rate me 5 stars first (before you rate anyone else)

A combination lock has a 1.5cm -diameter knob that is part of the dial you turn to unlock the lock. To turn that knob, you grip it between your thumb and forefinger with a force of 0.66N as you twist your wrist. Suppose the coefficient of static friction between the knob and your fingers is only 0.13 because some oil accidentally got onto the knob.What is the most torque you can exert on the knob without having it slip between your fingers?   

Amswer

torque = coefficient of static friction x force x radial distance = 0.13 x 0.66 x (1.5 x 10^-3)2 = 0.006435 Nm = 6.435 x 10^-3 N m Ans   

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