How to motivate a student to attempt solving tough questions? In any tutorial class some students seem to get frustrated with little tougher questions. While tackling them is important to learn the subject. How to motivate the students to attempt tougher questions without getting discouraged ?
This is a tough question and one that teachers have struggled with throughout the history of pedagogy.  Sometimes, students need to find within themselves the curiosity and drive to plow forward despite the frustration.  So, don't be discouraged when you see frustrated students, as every teacher has to deal with this.  Philosophy aside, here are some tips I've found helpful over the years:


Scaffolding is immensely important.  Build up to the harder problems, and give students the time they need to process how typical problems are solved.  E.g., If you're studying friction, have the students do plenty of problems that involve friction on a flat surface, then move to friction on a ramp, then work on friction on a vertical wall (by a sideways force), then move to centripetal friction that keeps a turning car from sliding off a road, then move to cars on banked hills.
Don't try to cover too much material in one sitting.  Students can only process so much at once, and many really do need time to process.
Positive feedback goes a long way.  When a student makes progression on a problem, acknowledge it.
Be available for help, but not always available.  Some students like the easy way out, which is to ask you how to do the problem!  Don't be afraid to turn a student away until they've given it a decent try.  That said, judicious pointers in the right direction can help.
Encourage them to work in groups.  This does run into the "easy way out" for some students, but more often it can lead to good ideas being generated, and students can learn from the collaboration.
Give them lots and lots of examples.  The more they see problem-solving techniques, the better they will become.


Unfortunately, given the time constraints of college teaching, it isn't always possible to use all of these strategies--I found that it was easier to find the time when I taught high school.  That said, students in college should be willing to work harder on their own, anyway (but we all know that isn't always the case!).