I am interested in a building a web app that displays, for every new visitor, a specific set of questions to be answered. The set of questions to be displayed are selected from a pool of database and are not supposed to be the same for every visitor. More precisely, the questions are selected based on the set of answers already received from previous workers. For e.g., if the goal is to get only n answers (from n different visitors) for every question, then the app should check how many answers have been collected for a given question already and select new questions accordingly. Is wordpress suitable for building this kind of app ? If yes, please point to the appropriate resources (docs/plugins etc). If not, do you recommend any other framework or writing code from scratch (for e.g. in PHP/MySQL) is the only option ? I am not very comfortable with rails and is perhaps an overkill for such a simple application.
You can use WordPress to save you some time. The structure of WordPress admin can be a time saving when you need to offer the client a panel to access some info, or control something.
You can use WordPress plugins to do, like, half of the work or more. You will still need to tweak the code, but it's faster than developing from scratch.
If you have the knowledge and the time, you can develop it from scratch and is probably better if you do so. But that actually is the result of what the client need, what time you have, the budget of the project, your knowledge, and etc.
If you decide to use WordPress, It's probably best to get a template or a framework to save you some time and work. You can install one of the many pool plugins for WordPress and tweak it around. A good free option would be https://wordpress.org/plugins/yop-poll/