(question) a 100 kg rock sits on top of a 80-meter cliff. if the rock falls, how fast is it going at 20 m? ignore air resistance.

When you push downward on a book at rest on a table, you feel an upward force. does this force depend on friction? defend your answer.

Astone is dropped from a cliff and falls 9.44 meters. what is the speed of the stone when it reaches the ground? a. 13.6 m/sec b. 1.39 m/sec c. 185 m/sec d. 9.80 m/sec

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