PHYSICS! A level Modular Questions,Turing Effects(A LEVEL的一道物理题,帮我解答一下,谢）

题目

PHYSICS! A level Modular Questions,Turing Effects(A LEVEL的一道物理题,帮我解答一下,谢）
A uniform metal bar is 2.4m long and is suspended from a factory ceiling by a chain at a distance of 60cm from one of the ends. The point at which the chain is attached to the bar is referred to as ‘x'. A 5000N weight is attached at the end closest to point ‘x' and a 1000N weight is attached at the other end of the bar, i.e. 180cm from point ‘x'. By taking moments about ‘x', show that, for the bar to lie horizontally, the mass of the bar must be 200kg,
第二问： What will the tension be in the chain for the example above?

答案

1.假设每单位长度的质量为ρ,则m=2.4ρ
依题意有等式如下
5000*0.6+0.3*0.6ρg=1.8*0.9ρg+1000*1.8
取g=10 m/s^2
解得ρ=250/3 kg/m
m=2.4ρ=200kg
2.F=5000+1000+mg=8000N