Q no 8 give me the explanation why is it so

Q8. Some statements about friction are given as 

(I) frictional force can accelerate a body.
(II) Frictional force is proportional to the area of contact between the two surfaces.
(III) KInetic friction is always greater than static friction.

(A) Only I is true.                                (B) Only (III) is true.

(C) I & II are true.                               (D) II & (III) are true.
Sol.              A

Dear student, 
​Please find below the solution to the asked query        

I. Friction slows down the motion of an object and any change in speed  provides acceleration. Hence, friction provides acceleration.

II. Friction force is independent of the area of contact. It depends on the nature of the surfaces in contact and the force acting between them.  â€‹

III. Kinetic friction is always less than the static friction.

Static friction comes is experienced on an object is at rest. Kinetic friction is experienced when the object is in motion. 

This would mean that static friction would be more as it keeps an object firmly at rest. The magnitude of the static friction keeps changing in response to the external force applied. However, if enough force is applied static friction is overcome and kinetic friction comes in to play. Kinetic friction is thus less as it allows an object to move.

 Hence, option A i.e. only I is true.
Hope this information will clear your doubts about the topic.   
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