a mass of 100 gram is attached to the end of a rubber string 49 cm long and having an area of cross section 20 sq. mm. the string is whirled round, horizontally at a constant speed of 40 r.p.s. in a circle of radius 51 cm. find the Young's modulus of rubber. explain the answer also.

Given that,

 

L = 49 cm

l = 51 - 49 = 2 cm

Cross sectional area a  20 mm² = 0.2 cm²

m = 100 g

R = 51 cm

ω = 40 r.p.s = 80 π rad s^-1

 

When the mass attached to the string is whirled, the length of the string increases under the effect of centrifugal force.

 

The centrifugal force F = mRω²

                                = 100 x 51 x (80 π)²