Which of the followWhich of the following examples in nature represents a chemical change?ing examples in nature represents a chemical change?

For the car in the picture ,in which direction is the normal force? -into the screen -down -out of the screen -up

It is really hard for me right know

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