Kinematics Question 737

Question: A mass of 2 kg it’s whirled in a horizontal circle by means of a string at an initial speed of 5 revolutions per minute. Keeping the radius constant the tension in the string is doubled. The new speed is nearly [MP PMT/PET 1998; JIPMER 2000]

Options:

A) 14 rpm

B)10 rpm

C) 2.25 rpm

D)7 rpm

Show Answer

Answer:

Correct Answer: D

Solution:

Tension in the string $ T=m{{\omega }^{2}}r=4{{\pi }^{2}}n^{2}mr $ $ T\propto n^{2} $

therefore $ \frac{n _{2}}{n _{1}}=\sqrt{\frac{T _{2}}{T _{1}}} $

therefore $ n _{2}=5\sqrt{\frac{2T}{T}}=7rpm $



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