Question

A block of mass 100 g moved with a speed of 5 m/s at the highest point in a closed circular tube of radius 10 cm kept in a vertical plane. The cross-section of the tube is such that the block just fits in it. The block makes several oscillations inside the tube and finally steps at the lowest point. The work done by the tube on the block during the process is :

• A. 1.45 J
• B. – 1.45 J
• C. 0.2 J
• D. zero

Answer 1

The correct option is B – 1.45 J

$\text{From, work-energy theorem}{\text{W}}_{\text{net}}=△\text{KE}\text{mg}\times \text{2R}+{\text{W}}_{\text{friction}}=0-\frac{1}{2}{\text{mv}}^2\therefore {\text{W}}_{\text{friction}}=-\frac{1}{2}\times (100\times {10}^{-3})\times 5^2-(100\times {10}^{-3})\times 10\times 10\times {10}^{-2}\times 3=-1.25-0.2=-1.45J$