Why is it easier to push a heavy block from behind than to press it on the top and push?

Why is not possible to push a car from inside

It is easier to roll barrel than to pull it along the road why

Why is it easier for you to float in salt water than in fresh water?

Why is it easier to swim in sea water than in river water?

Why is it easier to stop a lightly loaded truck than heavier one that has equal speed

Why is it easier to carry the same amount of water in two buckets, one in each hand rather than in a single bucket?

Two blocks A and B of mass m_A and m_B respectively are kept in contact on a frictionless table. The experimenter pushes the block A from behind so that the blocks accelerate. If the block A exerts a fore F on the block B, what is the force exerted by the experimenter on A?

small block of mass 200 g is kept at the top of a frictionless incline which is 10 m long and 3.2 m high. How much work was required to lift the block from the ground nd put it at the top .