EXAM 3                  December 2, 1988            PS 207    

  If you need a constant not given here or do not understand a problem,  
please ask me about it.  Remember to include diagrams and explain your  
reasoning.  No notes, books, etc. may be used during this exam.   

               2
  g = 9.8 m/sec 
                                       -31
  The mass of the electron is 9.11 x 10    kg    

  1.  (From homework)  A person of mass  m  is standing at the rear  

of an iceboat of mass  M  and length  L  that is moving at a speed of   

v   across ice that may be considered to be frictionless.  He decides to  
 0
walk to the front of the boat and does so at a speed of  u  with respect  

to the boat.  How far did the boat move across the ice while he was  

walking?   

  2.  A meter stick is leaning against a wall, making an angle of  theta   

with the wall.  The coefficient of static friction between the stick and  

either the wall or the floor is  mu  .  How hard can you press down  
                                   s
vertically on the top of the stick before the stick begins to slip?   


  3.  To determine the moment of inertia  I  for a huge motor, the  

motor is twice brought up to its operating speed of  omega  and then  
                                                          0
allowed to coast to a stop.  The first time, when only friction stops  

it, the time taken is  t .  When an extra retarding torque of  tau   is  
                        1                                         2  
 
added, it takes a time  t  to stop.  What is the moment of inertia of  
                         2
the motor?   


  4.  Two billiard balls are placed in contact on a smooth,

frictionless table.  A third ball moves toward this pair with

velocity    v  in the direction shown in the diagram [perpendicular

to the line connecting the stationary two].  What will be the

velocity (magnitude and   direction or components) of the three

balls after the collision?  The balls are identical and the

collisions essentially elastic.