Posts Tagged ‘ANSWERS TO QUESTIONS FROM VISITORS’

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helium balloon raises up slowly through air .why?

Helium balloon raises up slowly through air .why?
(Question posted by Siju)

Helium is lighter than air and therefore the buoyant force (the upward force exerted by air on the balloon) will be more than the weight of the He filled balloon. So it rises up.

As it begins to move upwards, frictional forces (viscous force) also come into play which increase with increase in speed and soon the net downward force becomes equal to the downward force and thereafter the balloon rises up with a constant velocity.

A Question from Heat and Thermodynamics

A thermo stated chamber at a height ‘h’ above the earth’s surface and maintained at 30 degree Celsius has a clock fitted with an uncompensated pendulum. The maker of the clock for the chamber mistakely designed it to maintain correct time at 20 degree Celsius. It is found that if the chamber were brought to earth’s surface the clock in it would click correct time. The coefficient of linear expansion of the material of pendulum will be………………..

- Himani

A question from waves

Question: A string in a musical instrument is 50cm long and its fundamental frequency is 800 Hz. if a frequency of 1000 Hz is to be produced then the required length of the string is………………

Answer:

When the string vibrates in single loop, its frequency corresponds to its fundamental frequency.

In this case two nodes are produced at the two ends and it corresponds to half the wavelength.

i.e. wavelength = 50 x 2 = 100 cm = 1 m

And this corresponds to a frequency of 800 Hz

wavelength x frequency = speed of sound

The speed is constant in the same medium

Therefore a fundamental frequency of 1000 Hz, the length should be

L = 50*800/1000 = 40 cm

If you are familiar with the above ideas you could simply take

f1L1 = f2 L2

and solve the problem