In three experiments, three different horizontal forces are applied to the same block lying on the same countertop. The force magnitudes are F1 = 12 N, F2 = 8 N, and F3 = 4 N. In each experiment, the block remains stationary in spite of the applied force. Rank the forces according to (a) the magnitude fs of the static frictional force on the block from the countertop and (b) the maximum value fs, max of that force, greatest first.

Explanation:

The fores of magnitude F₁ = 12 N

The frictional force is self adjusting force , and it acts opposite to the applied force .

In this case , the force of friction f = 12 N

Similarly in second case  , the force of friction f = 8 N

and in third case the force of friction f = 4 N

( a ) The counter top from beginning

4 N , 8 N and 12 N

( b ) The maximum force applied is 12 N , thus maximum force of static friction is also 12 N

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