Question

A: A block of mass 5 kg lies on a table. The coefficients of static and kinetic froctions are 0.4 and 0.3 respectively. You exert a horizontal force of 17 N. The acceleration of the block is:

B: An elevator has a frayed cable which will break if the tension exceeds a certain value. Is the tension more likely to exceed this value if the elevator is :

a)accelerating upward

b)the motion is irrelevant  

c)moving at constant velocity

d)accelerating downward

Answer 1

Concept - since the block in at rest, to move the block the applied force is must be greater than the maximum static friction force. We find the maximum static fiction force and see that it is more than the applied force and hence the block will not move and acceleration will be zero.

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