When your head sticks out of the water the upthrust reduces as your head is no longer displacing water, and there is 0 resultant force so you float at that level. hope this helps, can i get brainliest please
Answer:

Explanation:
Age of the universe = 
Lifetime of a top quark = 
Top quark life would be given by

Hence, the answer is 
Answer:
the time required for the sound to travel between the whales 0.66 S.
Explanation:
As given in the problem, the velocity of sound wave (
) is governed by the equation

Given,
and 
So for salt water, the velocity of sound wave (
) can be written as

As the whales are d = 1 Km or 1000 m apart from each other, so the time (
) required for the sound wave to travel this distance is given by

It is b exothermic cause it in a system increases the reaction is considered to be b.