Theory of Machine
Which of the following statements regarding laws governing the friction between dry surfaces are correct?

The friction force is dependent on the materials of the contact surfaces.
The friction force is directly proportional to the normal force.
The friction force is independent of me area of contact.
All of these

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Theory of Machine
Crowning on pulleys helps

In decreasing the slip of the belt
In increasing velocity ratio
For automatic adjustment of belt position so that belt runs centrally
Increase belt and pulley life

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Theory of Machine
The contact ratio is given by

(Length of the arc of contact)/(Circular pitch)
(Length of the arc of approach)/cosφ
(Length of path of recess)/(Circular pitch)
(Length of the path of approach)/(Circular pitch)

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