Q. The twisting couple per unit twist for a solid cylinder of radius 3 cm is 0.1 N-m. The twisting couple per unit twist, for a hollow cylinder of same material with outer and inner radius 5 cm and 4 cm respectively will be
A) 0.1 N-m
B) 0.455 N-m
C) 0.91 N-m
D) 1.82 N-m
Explanation
(b) Twisting coupler per unit twist for solid cylinder, for hollow cylinder, $C_{1} = \frac{\pi\eta r^{4}}{2l}$
$\therefore\ \ C_{2} = C_{1}\frac{r_{2}^{4} - r_{1}^{4}}{r^{4}} = \frac{0.1\ \times \left( 5^{4} - 4^{4} \right)}{\partial^{4}} = \frac{36.9}{81}$
= 0.455 Nm
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.