Q 11-05-018NEETJEE MainEAMCET 2013 (Engineering)Hard
A block of mass $2.9$ kg is suspended from a string of length $50$ cm and is at rest. Another block of mass $100$ g, which is moving with a speed of $150$ m/s, strikes and sticks to the first block. Subsequently, when the string makes an angle of $60°$ with the vertical, the tension in the string will be ($g = 10\ \text{m s}^{-2}$)
Answer: (B) $135$ N
Concept. Momentum in the collision, energy during the swing, radial equation at $60°$.
Step 1. Collision. $0.1 \times 150 = 3v \Rightarrow v = 5$ m/s.
Step 2. At $60°$. Rise $0.25$ m: $v'^2 = 25 - 5 = 20$.
Step 3. Tension. $T = mg\cos60° + \dfrac{mv'^2}{l} = 15 + 120 = 135$ N.
Answer. $135$ N (Option B).
Solution by Sreeraj P, M.Sc Physics