HRW PROBLEM SUPPLEMENT #1 - CHAPTER 7
  41.  If a ski lift raises 100 passengers averaging 660 N in
       weight to a height of 150 m in 60 s, at constant speed,
       what average power is required of the force making the
       lift?
 
  43.  In Fig. 7-10(a), a block of mass m lies on a horizontal
       frictionless surface and is attached to one end of a
       horizontal spring (with spring constant k) whose other
       end is fixed.  The block is initially at rest at the
       position where the spring is unstretched (x = 0) when
       a constant horizontal force F in the positive direction 
       of the x-axis is applied to it.  A plot of the resulting
       kinetic energy of the block versus its position shows
       that the block attains a maximum kinetic energy of 4.0 J
       at the location x = 1.0 m (so the acceleration is zero
       at that location).  (a) What is the magnitude of F?
       (b) What is the value of the spring constant k?

  49.  A 230 kg crate hangs from the end of a 12.0 m rope.  You
       push horizontally on the crate with a varying force F to
       move it 4.00 m to the side (the rope stays tight during
       the push so that the final angle between the rope and the
       vertical is 19.5 degrees). (a) What is the magnitude of F
       when the crate is in this final position?  During the
       crate's displacement, what are (b) the total work done on 
       it, (c) the work done by the gravitational force on the 
       crate, and (d) the work done by the pull on the crate from 
       the rope? (e) Knowing that the crate is motionless before 
       and after its displacement, use the answers to (b), (c), 
       and (d) to find the work your force F does on the crate.  
      (f) Why is the work of your force not equal to the product 
       of the horizontal displacement and the answer to (a)?

  50.  A frightened child is restrained by her mother as the 
       child slides down a frictionless playground slide.  If 
       the mother exerts a force of 100 N up the slide on the
       child,  the child's kinetic energy increases by 30 J as
       she moves down the slide a distance of 1.8 m.  (a) How 
       much work is done on the child by the gravitational 
       force during the 1.8 m descent?  (b) If the child is not 
       restrained by her mother, how much will the child's 
       kinetic energy increase as she comes down the slide that 
       same distance of 1.8 m?

       SERWAY - CHAPTER 7
  22.  When a 4-kg mass is hung vertically on a certain light
       spring that obeys Hooke's law, the spring stretches
       2.5 cm.  If the 4-kg mass is removed, (a) how far will
       the spring stretch if a 1.5-kg mass is hung on it, and
       (b) how much work must an external agent do to stretch
       the same spring 4.0 cm from its unstretched position?

  26.  If it takes 4 J of work to stretch a Hooke's-law spring
       10 cm beyond its unstressed length, determine the
       additional work required to stretch it another 10 cm.

       FISHBANE - CHAPTER 6
  57.  Electricity costs about $0.08 per kWh.  Your monthly
       electric bill is $26.00.  Assuming that your only use of 
       electricity is for light and that you keep your house lit 
       5 h/d, how many 100 W light bulbs do you keep going?

  63.  The maximum power of a particular horse is 1 hp.  With
       what speed can this horse pull a sled on level ground if
       the weight of the sled with its load is 5000 N and if the
       coefficient of kinetic friction is mu_k = 0.03?  What is
       the maximum speed on a 5 degree upward incline?

  65.  A waterfall, whose height is 40 m, has 200 cubic meters
       of water falling every second.  If the waterfall is used
       to produce electricity in a power station, and if the
       efficiency of conversion of kinetic energy of falling
       water to electrical energy is 60 percent, what is the 
       power production of the station?

       PROBLEM A2
   2.  Consider again the "Tarzan question" from Ch. 5 (#23).
       Use the Work-Kinetic-Energy Theorem to show that 
       4.62 m/s is the correct speed for Tarzan when he has
       swung from 22 degrees (where v = 0) to 11 degrees.