Sample 1Medium
A figure shows a small stone tied to a light string of length 0.5 m and whirled in a vertical circle about a fixed point. The lowest point is marked L and the highest point H. Take g = 10 m/s². What is the minimum speed at L for which the stone just completes the circle with the string taut?
Show the answer
The answer is C.
At H the minimum speed is √(gr); energy conservation from L to H (rise 2r) gives v_L = √(5gr) = √(5 × 10 × 0.5) = 5 m/s.
- A.
2.2 m/s is √(gr), the minimum speed at the top, not at the bottom.
- B.
3.9 m/s is √(3gr), which omits part of the energy needed to rise 2r.
- D.
7.1 m/s is √(10gr), more than the minimum required.
NCERT: Class 11 Physics, Chapter 5