A set of stadium stairs consist of 90, 20 cm high steps. A 70 kg runner is training by traversing up and down the steps. a. What is the change of potential energy that occurs with each step? For all 90 steps? b. How much work is required to travel up the steps in 20 sec? In 15 sec? c. What is the power required to run up the steps in 20 sec? In 15 sec? d. What is the total work done over the course of the stadium training session? Why?

A 5.00 gram bullet moving horizontally with a speed of 400 m/s collides with a wooden block. After moving 2.00 cm into the block the bullet stops moving. Was work done on the bullet? If so describe the type of work and the force that did the work.     a. yes, negative work, force is in the opposite direction as the initial velocity of the bullet   b. yes, positive work, force is in the same direction as the initial velocity of the bullet   c. yes, positive work, force is in the opposite direction as the initial velocity of the bullet   d. No work was done on the bullet   e. yes, negative work, force is in the same direction as the initial velocity of the bullet

2. A 900 kg elevator is raised by an electric motor up from the basement to the third floor, a vertical distance of 9.9 m, over the course of 5 s. There's a friction force of 125 N between the elevator and the elevator shaft. A. Draw a free body diagram of the elevator. Which forces are conservative? Which forces are dissipative? Which are external? B. How much potential energy does the elevator gain as its lifted? C. What is the work done by friction on the elevator? Is it positive or negative?

A spring with spring constant k is attached to the floor, standing vertically. You place a box of mass m on the spring and, from rest, release it. The spring bounces up and down a few times and comes to rest (both its velocity and acceleration are zero). Find the thermal energy generated in this process in terms of m, g, and k. Answer Options: A. mg/k   B. m^2 g/k C. m^2 g^2/k   D. m^2 g^2/ 2k   E. mg/2k