laminar flow questions

8/13/2019 Laminar Flow Questions

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1. A sign at a railway station advises passengers to keep back from the platform edge. This is

because passing trains may cause turbulence.

Explain what is meant by turbulent flow, and suggest why it is dangerous for passengers to

stand near the edge of the platform.

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Ashlyns school 1


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2. A childs birthday balloon is filled with helium to make it rise. A ribbon is tied to it, holding a

small plastic mass designed to prevent the balloon from floating away.

P l a s t i c m a s s

a! Add labelled arrows to the diagram of the balloon to show the forces acting on the

balloon.(2)

b! The balloon is approximately a sphere, of diameter "# cm. $how that the upthrust on the

balloon is about #.% &.

The density of the surrounding air ' (."# kg m)"

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Ashlyns school 2


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c! The ribbon is cut and the balloon begins to rise slowly.

i! $ketch a diagram to show the airflow around the balloon as it rises.

(1)

ii! *hat is the name of this type of airflow+

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d! A student suggests that if the balloon reaches terminal velocity, its motion could be

described by the relationship

mg -r'gr

".

"

/

where ' viscosity of air, m' mass of the balloon, r' radius of the balloon and v' the

terminal velocity reached.

i! *rite the above relationship as a word e0uation.

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Ashlyns school 3


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ii! The balloon has a total weight of #.(1 &. 2se the e0uation given above to calculate

the corresponding value for the terminal velocity of the balloon.

3iscosity of air ' (.4 5 (#)6

& s m)%

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Terminal velocity ' .........................................................(3)

iii! $uggest a reason why the balloon is not likely to reach this calculated velocity.

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(Total 12 marks)

3. 3olcanoes vary considerably in the strength of their eruptions. A ma7or factor in determining theseverity of the eruption is the viscosity of the magma material. 8agma with a high viscosity

acts as a plug in the volcano allowing very high pressures to build up. *hen the volcano finally

erupts it is very explosive. 9nce magma is out of the volcano it is called lava.

a! :ow would the flow of high viscosity lava differ from that of lava with a low viscosity+

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Ashlyns school 4


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b! *hat would need to be measured to make a simple comparison between the viscosities of

two lava flows+

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(1)

c! *hen the lava is exposed to the atmosphere it cools rapidly. *hat effect would you

expect this cooling to have on the lavas viscosity+

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d! *hen lava is fast flowing, changes to its viscosity disrupt the flow, making it no longerlaminar. 2se labelled diagrams to show the difference between laminar and turbulent

flow.

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Ashlyns school 5


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e! ;ifferent types of lava have different viscosities. The least viscous type has a viscosity of

about ( 5 (#"&s m

)%whereas a silica


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b! =elow is a list of material properties. $elect one that is desirable and one that is

undesirable for material from which the 7umpers skis are made. Explain your choices.

Elastic Tough Plastic

i! ;esirable property> ..........................................................................................

?eason> .............................................................................................................

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ii! 2ndesirable property> .......................................................................................

?eason> .............................................................................................................

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(Total 8 marks)

Ashlyns school 7

laminar flow questions

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