What if an inmate can't do any job due to health problems ? ( cant walk properly on his feet)? Will it affect him ? or his sentence will not be reduced ??

The staff does a good job of figuring out what jobs they can/will assign the inmates. There are clerical jobs, jobs in education, an orderly in the library and many other tasks that can be performed by the elderly, the injured or the disabled. They usually get everyone something to do. Jobs also benefit the inmates as they help get them into a routine which really makes the time go by faster.