EXAMPLES. 45 



17. Find the pressure on a square inch at a depth of 

 100 ft. in a lake, (1) neglecting, (2) taking account of the 

 atmospheric * pressure. Ans. (1) 43$ Ibs. ; (2) 58 Ibs. 



18. A reservoir of water is 200 ft. above the level of the 

 ground floor of a house ; find the pressure of the water, per 

 square inch, in a pipe at a height of 30 ft. above the ground 

 floor, neglecting atmospheric pressure. Ans. 73| Ibs. 



19. An equilateral triangular area is immersed vertically 

 in water with a side, one foot in length, in the surface. 

 Find the pressure upon it in ounces. Ans. 125 oz. 



20. A hollow cone, vertex upwards, is just filled with 

 liquid. Find (1) the pressure on its base, (2) the normal 

 pressure on its curved surface, (3) the vertical pressure on 

 the curved surface. [Let r = the radius of the base and 

 h = the altitude.] 



Ans. (I)#p7rr%; (2) gpnrhVr* + W', (3) 



21. A vertical rectangle has one side in the surface of a 

 liquid. Divide it by a horizontal line into two parts on 

 which the pressures are equal. 



Ans. If h be the vertical side, the depth of the horizontal 



h 



line = - 

 V2 



22. A vertical triangle, altitude h, has its base horizontal 

 and its vertex in the surface. Divide it by a horizontal line 

 into two parts on which the pressures are equal. 



Ans. The depth = - 



Vs 



23. A smooth vertical cylinder one foot in height and one 

 foot in diameter is filled with water, and closed by a heavy 

 piston weighing 4 Ibs. Find the whole pressure on its 



curved surface. 125?r 



Ans. 16 H - Ibs. 

 4 



* See Art. 11, Cor. g. 



