Question

By sucking through a straw , a boy can reduce the pressure in his lungs to 750mm of Hg (density= 13.6 g/cc) using a straw he can drink water from a max depth of ans: 13.6 ??

Answer 1

Normal pressure is 760 mmHg so the boy can create a depression of 10 mmHg in his lungs.  

According to the law of floatation  

Weight of floating body = weight of displaced liquid  

Wt. Of water displaced from glass = wt  of air of lung reduced (interm of mmHg) 

Wt of water displaced from glass = density of water (d1) x volume of water displaced (v1) 

Wt of air reduce from lung (interm of mmHg) = density of Hg(d2) x volume of air displaced (v2) 

Now d1 x v1 = d2 x v2 

And v1 = d2 x v2/d1 = 13.6 gcm –3 x10mm/ 1gcm –3 = 136mm = 13.6cm 

 

 

Density of water is 1gcm raise to power -3

Answer 2

Change in pressure is 10 mm of Hg

10 mm of Hg =1 Cm of Hg

Pressure = h × density × g

1 ×13.6 × g = depth × 1 × g

Depth = 13.6 cm