These questions consists of two statements each printed as Assertion and Reason. While answering these question you are required to choose any one of the following five reponses
(a) If both Assertion and Reason arecorrect and Reason is the correct explanation of Asserrtion.
(b) If both Assertion and Reason are correct but Reason is not the correct explanation of Assertion.
(c ) If Assertion is true but Reason is false.
(d) If Assertion is false but Reason is true.
Assertion A block of mass m starts moving on a rough horizontal surface with a velocity v. It stops due to friction between the block and the surface after moving through a certain distance.
The surface is now tilted to an angle of `30^(@)` with the horizontal and the same block is made to go up on the surface with the same initial velocity v. The decrease in the mechanical energy in the second situation is smaller than that in the first situation.
Reason The coefficient of friction between the block and the surface decreases with the increase in the anglle of inclination.

Answer

C

Explanation

(c ) Assertion Decrease in mechanical energy in case 1 will be
`DeltaU_(1)=(1)/(2)mv^(2)`
But decrease in mechanical energy in case 2 will be
`DeltaU_(2)=(1)/(2)mv^(2)-mgh`
`:. " " DeltaU_(2) lt DeltaU_(1)`
or assertion is correct.
Coefficient of friction is the mutual property of two surfaces. It does not depend on angle of inclination.