Page 115 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Assignment

1 Find the pressure at the depth of 40 metres below the surface of a lake in dynes per sq. cm., the
atmospheric pressure being neglected.
Solution:
Depth of water level ρ = 40 m = 4000 cm
Density of water d = 1 gram/cc
Acceleration due to gravity g = 980 cm/sec 2
Pressure below the surface of lake is given by the formula
= ρ.d.g.
Pressure = ρ.d.g
= 4000 x I x 980
= 3920000 dynes per sq. cm.

2 At 5 atmospheric pressure 0.2 cu. metre air is filled in a container. If the same air is filled at constant
temperature in a 1 cu. metre volume of container then calculate the air pressure in the container.
Solution: At constant temperature the gas follows Boyle’s Law
P V = P V 2
2
1
1
Here, P = 5, V = 0.2 cu. metre, V = 1 cu. metre
2
1
1
P V = P V
1 1 2 2
5 x 0.2 = P x 1.0
2
22
= × 1.5× 1.5
P = 7 = 1
2 49.5
Air pressure in the container = 1 atmospheric.
= = 7.07 mm 2
7
3 The volume of a gas at 770 mm pressure is 403 cc. Find the pressure when the volume is reduced to
22
1.5
1.5×
=
×
341 cc. 7
As per Boyles Law = 49.5 = 7.07 mm 2
7
P V = P V 2
1
2
1
770 x 403 = P x 341
1
P =
1
Pressure when volume is reduced = 910 mm

102

CITS : WCS - Mechanical - Exercise 10