Approaching research adviser with worries about project feasibility I'm a brand-new (read: started 3 weeks ago) Ph.D. student in Computer Engineering at an R1 institution in the U.S.  I was offered a position in a particular lab due to some prior experience I had on a topic of interest; my funding isn't tied to this particular lab though.  The faculty member heading the lab offered me the chance to start early and get a head start on research this summer, which I gladly accepted.

As I said, I'm about 3 weeks in now, and I'm starting to get worried about the feasibility of the task they've assigned to me.  Part of me wants to just chalk it up to my own inexperience and tell myself that it's nothing, but I had an unsettling experience with one of the other graduate students  recently.  Specifically, he told me that he had been originally assigned to work on the same task, and after some research he had concluded that it was infeasible at best (due to the sheer complexity of it) and a waste of time at worst (since even if it was completed, its performance would be terrible compared to existing applications).  This grad student is getting ready to graduate with his M.S., so he's not brand-new like I am.

So my questions are: (1) do my concerns about the feasibility of the task have any substance (given my inexperience with large research projects) and (2) if they do, how do I approach my adviser/faculty member with them?
Ultimately you are the judge but by the looks of it, I would consider 3 weeks as too early to decide if a task is feasible or not. I am assuming that you know the colleague who graduated just for 3 weeks. That is a short time to know someone and calibrate their opinions with your own understanding and capabilities. 

If the supervisor has given you the task despite the other colleague did not doing much on it there might be some weight in the task. I would suggest you do your own thorough investigation and give at least 3-4 more weeks trying to understand all aspects of the task at hand. Prepare a document and clearly mention what are the risks and opportunities in front of you, what are the related works surrounding the task.

At the same time, try to best gauge the intentions of involved folks, may be ask questions to other people around the lab, find experts online and write mails.

With this strategy, I think, at best you will lead to some groundbreaking ideas or findings and at worst you will learn a lesson in how to systemically conduct research, gauge opinions of others and strengthen the collaboration channels.

Hope this helps.