试题与答案

如图所示装置,滑轮A重40N,滑轮B、C各重20N,重物G=200N.求:不计拉

题型:问答题

题目:

如图所示装置,滑轮A重40N,滑轮B、C各重20N,重物G=200N.求:不计拉线质量及滑轮转动摩擦影响,绳自由端在力F作用下,恰能以60mm/s向下运动,则力F的大小是多少?重物G在1min内能上升多少距离?(绳子足够长)

答案:

(1)有三段绳子在拉动滑轮,故F=

1
3
(G+G)=
1
3
×(40N+200N)=80N

(2)1min内绳端上升S=V?t=0.06m/s×60s=3.6m

因有三段绳子在拉重物,故物体上升距离h=

1
3
S=
1
3
×3.6m=1.2m

答:拉力F为80N;重物上升1.2m.

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