Which is a suitable method to decrease friction?

In the given system,if $M_2 = 2M_1$,the tension in the string is $T$. If the positions of the blocks are interchanged,what will be the new tension in the string?

What is the value of the contact force $R$ on an object of mass $m$ placed on an inclined plane with angle $\theta$?

$Assertion$: Two bodies of masses $M$ and $m$ $(M > m)$ are allowed to fall from the same height. If the air resistance for each is the same,then both bodies will reach the Earth simultaneously.
$Reason$: For the same air resistance,the acceleration of both bodies will be the same.

$A$ block of mass $m$ is suspended by a light thread from an elevator. The elevator is accelerating upward with uniform acceleration $a$. The work done by tension on the block during $t$ seconds is $(u = 0)$.

Match the items in Column-$I$ with those in Column-$II$.

Column-$I$	Column-$II$
$(1)$ Definition of force	$(a)$ Newton's third law of motion
$(2)$ Measurement of force	$(b)$ Newton's second law of motion
	$(c)$ Newton's first law of motion