Question

Water flows through a horizontal pipe of which the cross – section is not constant. The
pressure is 1cm of mercury where the velocity is 0.35m/s. Find the pressure at a point
where the velocity is 0.65m/s.

Answer 1

so here your answer for this asked question
first of all let me know you that I have changed the unit from m/s to cm/s for my convenience


Bernouli’s eqn. would be still valid here.

Therefore,

Patm + pgh + 0.5pv^2 = Constant.

Now,

1g1 + 0.5*p35^2 = 1gh + 0.5p*65^2

gh = 1*10*1 + 0.5*1*35^2 –  0.5*1*65^2

gh = 1490 cm

h = 149 cm Hg.

So the pressure at that point will be 149 cm Hg
and convert it into metre its answer will be
1.49 m Hg

Answer 2

According to Bernoulli's eqn.

P + pgh + 1/2pv^2 = constant

1g+0.5p35^2=1gh+0.565^2

gh=1*10*1+0.5*1*35^2-0.5*1*65^2

gh=1490cm

h=1490/10=149cm

Or h=0.8cm of Hg.