1. Consider a rod of mass 1g and length L, held in place against a vertical wall by
a cable at the opposite end as shown in the diagram. A sign of mass 10kg is also
hanging o� the end of the rod furthest from the wall. The angles marked are �=30
�
and �=45
�
.
(a)Find the tension in the cable. (Hint: Is the mass of the rod neg-
ligible here? Then clearly mark your pivot point and start summing your
torques.) If the cable has a breaking point of 1000N, will it hold?
(b) Find the normal force from the wall on the rod and explain
whether or not there must also be friction between the wall and the rod in
this particular problem. If so, give the magnitude and direction of the friction
force required. (Hint: you will need to draw a diagram and sum the forces.
3 answers