作者EricTao (幻想风)
看板Physics
标题[问题] 一个力学习题
时间Sat Oct 25 22:37:16 2008
这是课本的题目，
A block of mass M is pulled along a horizontal (Fig)
┌──┐ m
frictionless surface by a rope of mass m, as │M ╞══→ F
─┴──┴─────
shown in Fig. A horizontal force F acts on one end
of the rope.
(a) Show that the rope must sag, even if only by
an imperceptible amount. Then, assuming that the
sag is negligible, find --
(b) the acceleration of the rope and the block, --
(c) the force on the block from the rope, and --
(d) the tension in the rope at its midpoint.
看不懂(a)要show绳子会松弛(sag)，我不懂为什麽会松弛，这样不就T=0吗?
还是我误解了题目的意思?
--
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◆ From: 118.166.118.184
1F：推 sukeda:绳子有重量，绳子如果绷紧，将无法有垂直的力抵销绳重 10/25 22:55
2F：→ EricTao:所以是下垂 而不是松弛的意思吗? 10/25 22:56
3F：推 sukeda:他的松弛只是指无法拉直吧 10/25 22:57
4F：→ EricTao:嗯...我查的英汉字典写松弛 让我会错意了ˊˋ 10/25 23:03