A random physics student in Colorado $($m $=80$ kg$),$ starting from rest, skis down a slope from a point that is $100$ m higher than the base, and the slope is inclined $30$ degrees from the horizontal. She drags her poles into the snow and she descends, creating a constant force of $150$ N which directly opposes her motion. What is this student's speed at the bottom of the hill? $($Use the conservation of energy!, and assume the slope is frictionless$)$