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7 Nov 2009 12:50:47 IST

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a barometer kept in an elevator accelerating upward reads 76 cm. Air pressure in elevator is a

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1.a barometer kept in an elevator accelerating upwardreads 76 cm. Air pressure in elevator isa)76cm b)<76cm c)>76cm d)0 . pls explain

2.)a solid is immersed in liquid ,The force exerted by the liquid on solid will

a)increase if it is pushed deeper inside the liquid

b)change if its orientation is changed

c)decrease if it is taken partially out of liquid

d)be in vertically upward direction

3) A closed vessel is half filled with water . There is a hole near the top of the vessel and air is pumped out from this hole.

a)The water level will rise up in the vessel.

b)the pressure at surface of water will decrease

explain why b)is correct but option a) is incorrect.

4)Water flows through 2 identical tubes A and B. A volume "V"of water passes through the tube A and 2V through B in a given time, which of the following may be correct?

a)flow in tubes are steady.

b)flow in both tubes are turbulent

c)flow is steady in A but turbulent in B

d)flow is steady in B but turbulent is A

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M. Fuaad Khan

Scorching goIITian

Joined: 10 Apr 2009

Posts: 223

8 Nov 2009 00:53:41 IST

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1. Initially mg = ρ g A h

In elevator m(g + a) = ρ (g + a) A h’

Upon dividing

(g + a) / g = (g + a) h’ / g h

h = h’

Hence height re g mains the same. So air pressure is 76 cm

2. F_b= ρ g A h = ρ g V

F_bµ Volume of Solid immersed

Hence V increases, F_bincreases and V decreases, F_bdecreases

At eq. F_b balances mg, hence acts vertically upwards

3. As air is taken out. the pressure above water dec. Because pressure exerted by air is dec as qty. of air dec.

But there is no change in height of water because above vaccum creation doesn't exert any force thus

not affecting height of water.

4. Turbulent or steady flow depends upon REYNOLD'S No. given by pdg / n(eeta). If we calculate it , then we don't know range of Reynolds no. for which flow is steady.

jit

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Joined: 3 Feb 2012

Posts: 1

3 Feb 2012 21:07:10 IST

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in verma ans of 1 is given c

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