A clothesline is hung between two poles. No matter how tightly the line is stretched, it
always sags a little at the center. Why?
Young and Freedman 4-43:
A train (engine + four cars) is speeding up with a
acceleration of magnitude |a|. If each ar has a mass m and each car has negligible
frictional forces acting on it, what is (a) the force of the engine on the first car? (b)
the force of the first car on the second car? (c) the force of the second car on the third
car? (d) the force of the fourth car on the third car?
Young and Freedman 5-19:
A 640 N physics student stands on a bathroom scale in an
elevator. As the elevator stars moving, the scale reads 800 N. (a) Find the acceleration
of the elevator (magnitude and direction). (b) What is the acceleration if the scale reads
450 N? (c) If the scale reads zero, should the student worry?
Is an astronaut in orbit about the earth in a weightless environment?
Young and Freedman 5-27:
A stockroom worker pushes a small crate with mass 9.40 kg
on a horizontal surface with a constant speed of 4.50 m/s. The coefficient of kinetic
friction between the crate and the surface is 0.20. (a) What horizontal force must be
applied by the worker to maintain the motion? (b) If the force calculated in part (a) is
removed, how soon does the crate come to rest?
if time permits -
For medical reasons it is important for astronauts in outer space to determine their
body mass at regular intervals. How could you measure body mass in an apparently
weightless environment.
Young and Freedman 5-34: Refer to figure 5-44 on page 154. The coefficient of
kinetic friction between block A (with weight Wa) and the table top is m k. Calculate the weight Wb of the hanging
block required if this block is to descend at constant speed once it has been set into
motion.