JEE Mains · Physics · STD 11 - Work,energy,power and collision
- JEE Mains 2026
- Hard
- MCQ
A small bob A of mass m is attached to a massless rigid rod of length 1m pivoted at point P and kept at an angle of \( 60^{\circ} \) with vertical as shown in figure. At distance of 1m below point P, an identical bob B is kept at rest on a smooth horizontal surface that extends to a circular track of radius R as shown in figure. If bob B just manages to complete the circular path of radius R upto a point Q after being hit elastically by both A, then radius R is ___________m.
Pick an option to check your answer.
Answer & Solution
Correct Answer
(B) \( \frac{1}{5} \)
Step-by-step Solution
Detailed explanation
\( V_{A} \) at lowest point
\( V_{A}=\sqrt{2g\ell(1-\cos \theta)} \)
\( V_{A}=\sqrt{2\times10\times1(1-\frac{1}{2})}=\sqrt{10} \)
After collision velocity of B becomes,
\( V_{A}=\sqrt{10}=V_{B} \) (Same mass)
Now to complete circular motion
\( V_{B}=\sqrt{5gR} \)
\( R=\frac{1}{5} \)
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