Question

A $1\, kg$ stone at the end of $1\, m$ long string is whirled in a vertical circle at constant speed of $4\, m / s$. The tension in the string is $6\, N$, when the stone at $\left(g=10\, m / s ^{2}\right)$

• A. top of the circle
• B. bottom of the circle
• C. half way down
• D. None of the above

Answer 1

Answer: (A)

top of the circle

Answer 2

The force on string $F =m g=1 \times 10$ $=10\, N$ Centripetal force $=\frac{m v^{2}}{r}=\frac{1 \times(4)^{2}}{1}=16$ Tension at the top of circle $=\frac{m v^{2}}{r}-m g=16-10=6\, N$ Tension at the bottom of circle $=\frac{m v^{2}}{r}+m g$ $=10+16=2.6\, N$