On a stationary sail-boat,air is blown at the sails from a fan attached to the boat. The boat will

In which of the following graphs,the total change in momentum is zero?

Two unequal masses $A$ and $B$ moving along a straight line are brought to rest by equal retarding forces. If $A$ takes double the time taken by $B$ to come to rest and $A$ travels $\frac{2}{3}$ of the distance covered by $B$ before coming to rest,then the ratio of masses of $A$ and $B$ is . . . . . . .

$A$ block is placed on a rough horizontal plane. $A$ time-dependent horizontal force $F = kt$ acts on the block,where $k$ is a positive constant. The acceleration-time graph of the block is

What force should be applied on the wedge so that the block over it does not move? (All surfaces are smooth)

Which is a suitable method to decrease friction?