Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement.  So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

30 lbs. x 10 ft. = 45 lbs. x 2 ft. + f_C x 6 ft.

300 ft. lbs. = 90 ft. lbs. + f_C x 6 ft.

f_C = \( \frac{300 ft. lbs. - 90 ft. lbs.}{6 ft.} \) = \( \frac{210 ft. lbs.}{6 ft.} \) = 35 lbs.