Answer:
a. 
b. 
Explanation:
I have attached an illustration of a solid disk with the respective forces applied, as stated in this question.
Forces applied to the solid disk include:

Other parameters given include:
Mass of solid disk, 
and radius of solid disk, 
a.) The formula for determining torque (
), is 
Hence the net torque produced by the two forces is given as a summation of both forces:

b.) The angular acceleration of the disk can be found thus:
using the formula for the Moment of Inertia of a solid disk;

where
= Mass of solid disk
and
= radius of solid disk
We then relate the torque and angular acceleration (
) with the formula:

Answer:
Explanation:
Let the thickness of the film is t and the refractive index of the material of film is n.
When light travels through a sheet of thickness t, the optical path traveled is nt.
When the path of one of slit is covered by a sheet of thickness t, the optical path becomes
x = ( n - 1) t
As the one fringe is shift, so the optical path changed by one wavelength.
i.e., x = λ
So, λ = ( n - 1) t
