I'm pretty sure its b but i need to know as fast as possible which statement best describes universal law a)it is in effect some of all time b)it is in effect all the time c)it changes over time d)it operates under specific conditions

Awater slide of length l has a vertical drop of h. abby's mass is m. an average friction force of magnitude f opposes her motion. she starts down the slide at initial speed vi. use work-energy ideas to develop an expression for her speed at the bottom of the slide. then evaluate your result using unit analysis and limiting case analysis. express your answer in terms of the variables h, m, l, vi, f and appropriate constants. vf v f