# Mechanics

• Oct 8th 2009, 02:31 PM
ramzel
Mechanics
Hi i am revising, exams in 2 week and i got stuck on this question

A light inextensible string hsa its e4nds attached to 2 fixed points A and B.... With A vertically above B, smooth ring, R of mass 0.8Kg is treaded on the string and is pulled by a horizontal force of magnitude x newton...The ring rests in equilibrium...

http://img59.imageshack.us/img59/5993/maths.png

Find tension in the string <<< What am i suppsed to find, what tension exactly ?

Value of X

I can work the triangles

by vectors, or trigonometry, i just dont know what to look for ?
• Oct 8th 2009, 10:09 PM
Hello ramzel
Quote:

Originally Posted by ramzel
Hi i am revising, exams in 2 week and i got stuck on this question

A light inextensible string hsa its e4nds attached to 2 fixed points A and B.... With A vertically above B, smooth ring, R of mass 0.8Kg is treaded on the string and is pulled by a horizontal force of magnitude x newton...The ring rests in equilibrium...

http://img59.imageshack.us/img59/5993/maths.png

Find tension in the string <<< What am i suppsed to find, what tension exactly ?

Value of X

I can work the triangles

by vectors, or trigonometry, i just dont know what to look for ?

I take it that the 50* and 20* in your diagram are the angles that the two sections of the string make with the horizontal.

The tension in the string is the same on either side of the ring, and acts upon the ring in a direction along each section of the string. So the ring is in equilibrium under the action of four forces:

1. its weight vertically downwards
2. the force $X$ horizontally
3. a tension, $T$ say, inclined at an angle $50^o$ above the horizontal
4. a tension $T$ inclined at an angle $20^o$ below the horizontal

Resolve vertically, and you can find $T$ directly without needing to involve $X$.