Rotating Vessel

A vessel of radius r r is rotated about the axis AB with angular velocity ω \omega such that the lowest point of the water surface is at a distance of 1 m from the bottom. Find the distance h h of the highest point of water level from the base. Assume that no water flows out of the vessel.

Details

  • R = 2 R=2 m
  • ω = 5 \omega = 5 rad/s


The answer is 6.

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6 solutions

Arghyanil Dey
Apr 23, 2014

Let, consider a point on the curved surface of water.

Let , the mass of the point is m.

The force acted on the mass m is F which makes an angle ¢ with the vertical

So that Fcos¢=mg

F s i n ¢ = m w 2 x Fsin¢=mw^2x

t a n ¢ = w 2 x / g tan¢=w^2x/g

d y / d x = w 2 x / g dy/dx=w^2x/g

Y = w 2 × x 2 / 2 g Y=w^2×x^2/2g [integrating both side]

Y = 5 m w = 5 , x = 2 , g = 10 Y=5m{w=5,x=2,g=10}

The height of the highest point from the base is =5+1=6m

why are we using Fsin¢=mw^2x??

Jessie JSK - 7 years, 1 month ago

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Consider,the coordinate axis along the line parallel to the side of the container {taken as y axis}& the horizontal line through the point {that point where the considered mass is situated} taken as x axis.[ I mean two perpendicular lines through that point]

Let, the force F makes an angle ¢ with the y axis. This means

Fcos¢ ballances mg& Fsin¢ ballances the centrifugal force mw^2x.

As the force makes an angle ¢ with the vertical, the tangent of the curve (water surface) makes the same angle with the x axis .So tan¢=dy/dx

(I think it is the sufficient explanation for you)

Arghyanil Dey - 7 years, 1 month ago
Tejas Rangnekar
Apr 17, 2014

Formula for the question is

Y= R 2 w 2 2 g \frac{R^{2}w^{2}}{2g} + \y m i n \y_{min} Substitute the given values in formula you get y minimum is 1 metre in the question

from where did u get this formula...can u derive it..please!!

Max B - 7 years, 1 month ago

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See my solution . I derived it.

Arghyanil Dey - 7 years, 1 month ago

wow. I derived this formula but for some reason ended up with 4g in the denominator instead of 2g.

A Former Brilliant Member - 7 years, 1 month ago
Alinjar Dan
Apr 23, 2014

dy/dx=w^2x/2g.THEN integrate it.

Why w^2x/2g?

See my solution.

Arghyanil Dey - 7 years, 1 month ago

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Sorry.I made mistake while writting.But I SOLVED IT RIGHT.

ALINJAR DAN - 7 years, 1 month ago

how can we use pressure method?i mean pressure at the lowest point and that at the same level vertically below the curved point?

Mohd Wasih - 7 years, 1 month ago

Applying Bernoulli's equation considering two points : one at the vertex of parabola and one at the edge of the tube where water is at highest position.

You will get h = 5 m , h h' = 5 m, h' \rightarrow height with respect to vertex of parabola.

Means from base it is 5 + 1 = 6 \boxed{5 + 1 = 6}

Abc Def
Apr 25, 2014

H(max)=h(min)+ (w^2).)R^2)/2g : g is acceleration due to gravity= 10m/s -->H = 1+ (5x5)(2x2)/2x10 ---> = 6

Sudipan Mallick
Apr 24, 2014

At first find the pressure on both the ends of the tube. Substrac two equations to get this formula H-h=w^2/2g(R^2). put the values and get the answer!

Fine!!! A new corner of thinking!!!!!!!!!!

Arghyanil Dey - 7 years, 1 month ago

Why is it that w^2*x is equivalent to acceleration Thanks

kierwin de dios - 7 years, 1 month ago

(5^2)(2^2)/2(9.81)=5.097+1=6.097 or 6.1 to be exact..

Kervin Golong - 11 months, 1 week ago

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