A clothesline is hung between two poles. No matter how tightly the line is stretched, it
always sags a little at the center. Why?
A train (engine + four cars) is speeding up with a acceleration of magnitude |a|. If
each car 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?
Is an astronaut in orbit about the earth in a weightless environment?
A "block and tackle" system of ropes and pulleys is often used to lift large
objects off the ground. What does such a system look like? How does it work? Why is it
very useful for lifting large objects?
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?
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.
Consider the system shown below. The coefficient of kinetic friction between block A
(with weight Wa) and the table top is m k.
(a) 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. (b) Suppose the coefficient of
static friction is m s = 0.4 and the mass of A is 30
kg and the mass of B is 2 kg. What is the force of friction on mass A now (assuming an
initial condition of no motion)? How will the system move as time increases?
