a few clarifications in sprint and scrum roles

It should not change. If the Sprint goal becomes invalid, then the Sprint is canceled. This is a destructive process that results in a good deal of waste, so it is rarely done. If the business model is unstable and results in changing priorities, consider a much shorter Sprint e.g. 1 week. If the work is largely unplanned in nature, Scrum might not be the best since it assumes a certain level of stability.

Anybody on the Scrum team may remove an impediment, though it remains the Scrum Master's job to be responsible for serving the Development Team this way. Many times, the SM will need to partner with the PO or developers in order to remove impediments.

Work can absolutely be added to the Sprint Backlog so long as the Sprint Goals is not threatened. Be sure to be transparent and communicative with the PO, since it's their responsibility to maximize the value of the Development teams work.

If you're asking, can the nature of the roles change, the answer is, "Not if you are to continue using Scrum." Scrum is specifically defined and requires each aspect of it's events, roles and artifacts as they are interdependent. However, as teams gain master of the principles of agility Scrum teaches, they may reach a state where they will desire to transcend Scrum. This is ultimately the goal of Scrum IMHO, to provide a practical working on of agility such that it may be used to improve the profession of software development.

> does the Product owner actively help the scrum master in removing impediments.

Yes, but think of it this way: the PO must actively help to maximize the team's delivery of value.

If the Scrum Master needs the PO's help to remove an impediment, then the PO would be wise to consider the impact of a failure to help on the value which can be produced.

Thank you, Jason and Ian. its clear now. And I passed PSM1 with 93.8% :)

As we work through a sprint, the development team might find the work more complex than anticipated or the estimated time falling short in which case we can work with PO to clarify scope for the sprint.

Is it fair to say - that's an example of change in sprint goal, or is that an expected adjustment to delivery in a specific direction/functionality/most useful items? I am keen to hear any thoughts on these.