The figure shows a uniform disc, with mass M = 2.4 kg and radius R= 20 cm, mounted on a fixed horizontal axle. A block of mass m = 1.2 kg hangs from a massless cord that is wrapped around the rim of the disc. The tension in the cord is

Options

A. 12 N
B. 20 N
C. 24 N
D. none of these

Answer

D

Explanation

From figure acceleration of block
mg – T = ma
`T= m (g - a)`
for unwrapping `a = alphaR`
torque of dics is `zeta = alpha R`
`zeta = RT = I_("disc") alpha`
`alpha = (RT)/(I_("dics"))` where, `I_("disc") = (MR^2)/2`
`alpha = (2T)/m`
from equation 1st
`T= m (g- 1)`
after solving this we get
`T = 6N`