Physics 311, Quiz #5

Stuntman Jackie runs off the roof of one building, moving horizontally at speed v. He flies across an alleyway of width 7.9 m and falls onto a staircase which is 12.2 m below his original position. Question 1 How long is Jackie in the air?

  Answer: The time it takes Jackie to fall 12.2 meters is

            - 12.2 m  =  vy * t  -  0.5 * (9.8 m/s^2) * t^2

                      =  - (4.9 m/s^2) t^2

          Solving for time t, we find

                  t   =  1.58 s

Question 2 At what speed v must Jackie run to land exactly on the staircase?

  Answer: His horizontal speed remains constant during flight, so

               7.9 m  =  vx * t

          Solving for t,

                  vx  =  5.01 m/s

Question 3 What is Jackie's speed when he lands?

  Answer:  His speed is a combination of horizontal and vertical components:

                  vx  =  5.01 m/s

                  vy  =  (-9.8 m/s^2) * (1.58 s)

                      =  15.5 m/s

           Total speed is

                  v   =  sqrt(vx*vx + vy*vy) 

                      =  16.3 m/s

This page maintained by Michael Richmond. Last modified Dec 18, 2001.