HC Verma - Concept of Physics - Part 1 - Friction - Q.28

My friend preparing for the IIT JEE asked me this question...

This problem tests :-

1. Free body diagram 
2. Pseudo force
3. Use of Constraint equations

A very interesting question..and a very simple solution..

Complete Free Body Diagram

Some Force equations

Force equations

Answer for Acceleration

Explaining Constraint Concept - used in above problem