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Kinetic Theory - Multiple Choice Questions

 

Q1. The height of a water barometer meauring atmospheric pressure at the surface of a lake is 10 m.

A diving bell of internal volume 6.0 m3 is lowered into the fresh water lake until the volume of the contained air is 4.0 m3.

Assuming the temperature of the air in the bell does not change, find how deep in metres the surface of the water in the bell is below the lake's surface.

A
5
B
20/3
C
15
D
50/3
E
25

P1 = 6.0 m3

V2 = 4.0 m3

P1 = 10 m H2O

P1V1 = P2V2

10 x 6.0 = P2 x 4.0

P2 = 15 m H2O

However the air suffers not only the pressure from the water but also atmospheric prssure so that 15m H2O pressure is composed of 10 m H2O from the atmosphere and 5 m H2O from the water it is immersed in - the answer is therefore choice A.

 

Q2. A gas molecule of mass m moving at velocity u collides at right angles with the side of a container and rebounds elastically.

Which one of the following statements concerning the motion of the molecule is incorrect?

A
The magnitude of the change in momentum of the molecule is zero.
B
The magnitude of the change in momentum of the molecule is 2mu.
C
The force exerted by the molecule on the side of the container is equal to the force exerted by the container on the molecule.
D
The change in kinetic energy of the molecule is zero.