Question

A mass of $2kg$ is tied to the end of a string of length 1m. It is, then, whirled in a vertical circle with a constant speed of $5\mspace{6mu} ms^{- 1}$. Given that $g = 10\mspace{6mu} ms^{- 2}$. At which of the following locations of tension in the string will be $70\mspace{6mu} N$

• A. At the top
• B. At the bottom
• C. When the string is horizontal
• D. At none of the above locations

Answer 1

Answer: (B)

At the bottom

Answer 2

Centrifugal force $F = \frac{mv^{2}}{r} = \frac{2 \times (5)^{2}}{1} = 50NewtonWeight = mg = 2 \times 10 = 20Newton$Tension = 70 N (sum of above two forces)

i.e. the mass is at the bottom of the vertical circular path