Acylindrical rod of mass m. length l and radius r has two cords wound around it whose ends are a
to the ceiling as shown. the rod is held horizontally with the two cords vertical. when the rod s mecase
cords unwind the rod rotates. find the tension in the cords as they unwind.

T = mg/6

Explanation:

Draw a free body diagram (see attached).  There are two tension forces acting upward at the edge of the cylinder, and weight at the center acting downwards.

The center rotates about the point where the cords touch the edge.  Sum the torques about that point:

∑τ = Iα

mgr = (1/2 mr² + mr²) α

mgr = 3/2 mr² α

g = 3/2 r α

α = 2g / (3r)

(Notice that you have to use parallel axis theorem to find the moment of inertia of the cylinder about the point on its edge rather than its center.)

Now, sum of the forces in the y direction:

∑F = ma

2T − mg = m (-a)

2T − mg = -ma

Since a = αr:

2T − mg = -mαr

Substituting expression for α:

2T − mg = -m (2g / (3r)) r

2T − mg = -2/3 mg

2T = 1/3 mg

T = 1/6 mg

The tension in each cord is mg/6.

10 neutrons is the answer

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -