The solution for fh has a singularity (that is, becomes infinitely large) at a certain angle θcritical. For any angle θ>θcritical , the expression for fh will be negative. However, a negative applied force fh would reverse the direction of friction acting on the lawnmower, and thus this is not a physically acceptable solution. In fact, the increased normal force at these large angles makes the force of friction too large to move the lawnmower at all.

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's. 

Ithink it's dissoulution

The answer should be d if i’m wrong i’ll change my answer and fix it for you