Please tell me, which book should I buy :Cengage physics mechanics part 1 by bm sharma or dc pandey mechanics part 1.

I have both the books and I suggest that you buy Cengage Mechanics. The books contains all types of problems containing problems which are easy to ones which are very difficult. The book contains sufficient examples and lot of problems along with solution of each problem. 

DC Pandey Mechanics contains mostly easy problems and most problems are almost same. If you solve even the examples of Cengage physics then you would become comfortable with mechanics and would be able to solve Iorodov, I am not exaggerating.