A reel of mass “m” and radius of gyration “k” is rolling down smoothly from rest with one end of the thread wound on it held in the ceiling as depicted in the figure below. considering the thickness of the thread and its mass negligible in comparison with the radius “r” of the hub and the reel mass “m”, symbol “g” represents the acceleration due to gravity.
- The linear acceleration of the reel is:
(a) $\frac{gr^{2}}{\left ( r^{2}+k^{2} \right )}$ 
(b) $\frac{gk^{2}}{\left ( r^{2}+k^{2} \right )}$ 
(c) $\frac{grk}{\left ( r^{2} +k^{^{2}}\right )}$ (d) $\frac{mgr^{2}}{\left ( r^{2}+k^{2} \right )}$ 
2 . The tension in threads is
(a) $\frac{mgr^{2}}{\left ( r^{2} +k^{2}\right )}$ (b) $\frac{mgk^{2}}{\left ( r^{2} +k^{2}\right )}$
(c) $\frac{mgrk}{\left ( r^{2} +k^{2}\right )}$ (d) $\frac{mg}{\left ( r^{2} +k^{2}\right )}$