Dinesh,
First of all, you need Contact Hours and not PDUs. The difference is simply that Contact Hours are required before you earn a certificate and PDUs are only required afterwards. And since you are preparing for the exam this means that they are called Contact Hours. (But it's really just a different word for pretty much the same thing.)
Second, for the RMP you need 30 Contact Hours in "Risk Management". This means that you need to receive 30 hours of training in specific topics that are related to risk management. Or as PMI puts it: "30 contact hours of formal education in the specialized area of project risk management".
For the PMP exam on the other hand you need 35 Contact Hours, and these hours can come from "general" project management training. So the training here can be about scheduling, cost, procurement, and also from risk.
This means that if you receive 5 hours of risk management training for your PMP exam preparation (= 5 Contact Hours), then you can apply those to your RMP as well. But you cannot apply any of the other contact hours that are not risk related.
