Answer:

Explanation:
Net external force that exerted on the block is given as

here we know that



now we have

so we have

now the force exerted by bigger block on smaller block is given as



now we know that two blocks will exert equal and opposite force on each other
so here the force exerted by 2 kg block on 4 kg block will be

That two ways are known as:
1) Series connection
2) Parallel connection
<span>Submarines are equipped with water tanks called ballast tanks that fill up to submerge the vessel. Emptying the tanks and filling them with air causes the submarine to surface.</span>