involve weight acting at the center of gravity, tensions in ropes or wires, compressional forces on rods or hinges, and frictional forces.
Commentary
The solutions to the problems in this lesson are rather formal; that is, all problem solutions follow a regular procedure, which, if done carefully, will almost always produce the desired result. After learning the general procedures and practicing on a few examples, you should find no difficulty in solving any problem in this lesson.The steps in the formal solution
procedure are summarized here for easy reference.
1. Draw an imaginary boundary separating the system under
consideration from its surroundings.
2. Draw vectors representing the magnitude, direction, and point of
application of all external forces to the system (in other words,
construct a free-body diagram).
3. Choose a convenient reference frame, resolve all of the external
forces along these axes, and then apply the first condition of
equilibrium.
4. Choose a convenient axis, evaluate all of the external torques
around it, and apply the second condition of equilibrium.The
resulting simultaneous equations can then be solved for the
desired quantities.

1. A block of mass M = 12.0 kg slides at constant velocitywhen pushed by a force of F = 50 N applied at q= 30[!]as shown in the diagram. Find the coefficient of sliding friction between the block and the floor.

2. A weight W is hung from the middle of a taut clothesline 20.0 m long. The weight causes the center to drop 0.50 m below the horizontal (assume the line stretches slightly). Find the tension in the line in terms of W.

3. A 2.50-kg mass is hung from the ceiling by a long rope. It is pulled to the side by a horizontal force of 10.0 N. Find the tension in the long rope and the angle it will make with the vertical.

4. A skydiver in free fall reaches a speed of 40 m/s before pulling the ripcord. When the parachute opens, the skydiver experiences an initial upward acceleration of 20 m/s². What equilibrium speed of descent will the