Questions

Ans.  Suppose the speed of boat in still water is x km/h and speed of stream is y km/h

Speedof boat in downstream = (x + y) km/h x+ y = 32 …(i) 

Speed of boat in upstream = (x – y) km/h

x – y = 28 …(ii)

Add. Eqs. (i) and (ii), we get 2x = 60

x = 30 km/h

Largest sea in the world is Philippine sea.

In the middle of the 6th centuryB.C, a powerful empire was established in Iran this empire which lasted over two centuries is known as the Achaemenid Empire. The founder of this Empire was Cyrus with his capital at pasargadae. In 539 B.C, cyrus defeated the Babylonians and extended his empire over a vast territory up to Asia Miner. His successor was Darius I (522-486 B.C).

Cotton Gin was invented by Eli Whitney in 1793, which is used to separate cotton seeds from cotton fiber.

Hence, it was an important invention because it dramatically reduced the amount of time it took to separate cotton seeds from cotton fiber.

No work done as there is no external external pressure in free expansion. 

Hence, Work done in a free expansion process is Zero.

Bicycle is a compound machine in the above given options. A compound machine is a machine that is formed by two or more simple machines.

Bologna University , founded in 1088 CE

Lime mortar is generally made with Hydraulic lime.