Q 11-05-048JEE MainMedium
A bob hangs from a light string $2$ m long. It is given a horizontal speed of $\sqrt{60}$ m/s at the lowest point. Find the tension in the string, in newtons, when the string becomes horizontal, if the mass of the bob is $0.5$ kg. ($g = 10\ \text{m/s}^2$)
Numerical value type. Enter your answer.
Answer: 5
Concept. Energy to the horizontal position; there tension alone gives the centripetal force.
Step 1. Speed. $v^2 = 60 - 40 = 20$.
Step 2. Tension. $\dfrac{0.5 \times 20}{2} = 5$ N.
Answer. $5$.
Solution by Sreeraj P, M.Sc Physics