The speed of a sub marine over sea surface is 30 knot per hour and below sea surface is 20 knots per hour. What is the average speed of the submarine if it is below water surface for 3/4th of her time of journey What is the average speed of the submarine if it is under water surface for 3/4th of the total distance covered by him.

The speed of a sub marine over sea surface is 30 knot per hour and bel

1.	The speed of a sub marine over sea surface is 30 knot per hour and below sea surface is 20 knots per hour. What is the average speed of the submarine if it is below water surface for 3/4th of her time of journey What is the average speed of the submarine if it is under water surface for 3/4th of the total distance covered by him.
Answer» 1)`V_(avg)`=(total distance/total distance) `=(30T/4+203T/4)/T=45/2` 2)Total distance=d `T_1=(3/4d)/20` `T_2=(1/4d)/30` `V_(avg)`=Total distance/total time `=D/((3/4D)/20+(1/4d)/30)` `=240/11` .