A sphere starts from rest and accelerates vertically downwards in a liquid. For the viscous force on the moving sphere, state its direction.
A sphere in a liquid starts from rest and accelerates vertically downwards. For the viscous force acting on the moving sphere, state how its magnitude varies, if it does.
A man weighing $750\,\text{N}$ stands $3.6\,\text{m}$ from end D of a horizontal uniform beam AD, as shown in Fig. 4.1. The beam has weight $380\,\text{N}$ and length $9.0\,\text{m}$. It is supported by an upward vertical force $F_B$ at pivot B and an upward vertical force $F_C$ at pivot C. Pivot B is $2.0\,\text{m}$ from end A and pivot C is $2.0\,\text{m}$ from end D. The beam is in equilibrium.
State the principle of moments in words.
Calculate $F_B$ by taking moments about pivot $C$.
The man moves towards end D. The beam is on the point of tipping when $F_B$ becomes zero. Determine the least distance $x$ from end D at which the man may stand without causing the beam to tip.