9th Class
Science
Time and Motion
Question Bank
Motion
question_answer
A 2 kg stone at the end of a string 1m long is whirled in a vertical circle. At some point its speed is 4 m/s. The tension of the string is 51.6 N at this instant. Therefore, the stone is
A) At the top of the circle
B) At the bottom of the circle
C) Half-way down
D) None of these
Correct Answer:
B
Solution :
At the top, \[T+mg=\frac{m{{v}^{2}}}{r}\] At the bottom, \[T'-mg=\frac{mv{{'}^{2}}}{r}\] \[\therefore \] \[T'-2\times 9.8=\frac{2\times {{(4)}^{2}}}{1}=32\] \[\Rightarrow \] \[T'=32+19.6=\mathbf{51}\mathbf{.6}\,\,\mathbf{N}\] Thus, stone is at the bottom of the circle