SUPPLEMENTARY QUESTIONS

FORCES: Equilibrium of Forces.

1. Coplanar forces , , act on a point mass A. State or show in a

labelled diagram, the condition for the mass to be in equilibrium.

2. Currents in the sea water cause the buoy to be displaced so that the

rope makes an angle of 35 with the vertical, as shown below.

The buoy may be considered to be acted upon by three forces, the

tension T in the rope, a horizontal force D and a vertical force V equal

to 600 N.

Determine the magnitude of D. [420 N]

3. A picture of weight 5 N is suspended from a hook on a wall by a cord

which has a breaking strength of 25 N. Initially (the figure on the left)

the picture is found to be too low; the cord is shortened, with the

intention of hanging the picture as in the figure on the right. However,

when the picture is replaced, the cord breaks immediately. Explain,

why the cord broke when supporting a load much less than its

breaking strength.

4. A weight of 100 N and a system of pulleys is used to apply a force in

leg traction as shown in the figure below. The magnitude of the force

can be changed by changing the angle . Determine the value of the

traction force applied to the leg if:

a. = 60 [100 N]

b. = 30 [173 N]

What is theoretically, the maximum value of the traction force using W

= 100 N? (use g = 10 m s-2) [200 N]