[" re of mass of the "],[qquad [," A flubical block of mass "M" and edge a "],[" slides down a rough inclined plane of "],[" inclination "theta" with a uniform velocity.The "],[" torque of the normal force on the block "],[" torque of the normal force on the block "],[" about its centre has a magnitude "],[" (a) zero "," (b) Mga "],[" (c) Mga sin "theta," (d) "(1)/(2)" Mga sin "theta]]