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A barometer tube of negligible mass is suspended from a spring balance as shown. The mass of mercury in the tube is m and atmospheric pressure is p₀ . The cross section area of tube is A. What is the reading of spring balance ?
( my diagram is not that good.....pls manage [4])

#Physics #General Physics

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8 Answers

11

virang1 Jhaveri ·2009-03-08 22:53:31

mg + pA

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11

virang1 Jhaveri ·2009-03-08 22:53:47

Is it rite?

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11

virang1 Jhaveri ·2009-03-08 23:01:17

spring balance measure weight or mass?

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11

virang1 Jhaveri ·2009-03-08 23:05:40

i feel it measures weight.

Therefore mg is the weight of the mercury. The additional force by Pressure is pA

I feel therefore my answer is rite

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62

Lokesh Verma ·2009-03-08 23:15:00

Hint draw the FBD of the air column in the tube!

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11

virang1 Jhaveri ·2009-03-08 23:59:47

Cannot get it pls help sir.

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62

Lokesh Verma ·2009-03-10 03:53:34

pressure inside will be

P-ÏgH

=P-mg/A

difference in pressure on the top surface of the tube is P-(P-mg/A)

=mg/A

I think this should be the reading on the spring balance

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62

Lokesh Verma ·2009-03-10 03:53:56

because there is no other force acting anywhere on the tube..

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