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 $
