Physics
It is easier to roll a barrel full of coal tar than to pull it because

the full weight of the barrel comes into play when it is pulled
the rolling friction is much less than the sliding friction
more surface area of the barrel is in contact with the road when it is pulled
coal tar is a liquid and it flows in the barrel when it is rolled

ANSWER DOWNLOAD EXAMIANS APP

Physics
On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because:

cohesion of water is greater than its adhesion with glass.
density of mercury is greater than that of water.
cohesion of mercury is greater than its adhesion with glass.
mercury is a metal.

ANSWER DOWNLOAD EXAMIANS APP
MORE MCQ ON Physics