Tension in the String

1. Oct 9, 2012

risepj

1. The problem statement, all variables and given/known data

"What is the tension in the string?"

• .5kg block
• Suspended at the midpoint of a 1.25m-long string
• Ends of string attached to ceiling are 1m apart.

2. Relevant equations

cosθ, sinθ, tanθ

T$_1$$_x$+T$_2$$_x$+F$_g$$_x$=ma$_x$

T$_1$$_y$+T$_2$$_y$+F$_g$$_y$ = T$_1$$_y$+T$_2$$_y$- F$_g$ = ma$_x$

3. The attempt at a solution

My homework is online and immediately verifies whether or not your answers are correct. I was able to solve that the angle the string makes with the ceiling is 36.87°.

From there, I attempted to solve for T$_1$ and T$_2$ as follows:

T$_1$$_x$+T$_2$$_x$+F$_g$$_x$=ma$_x$.

⇔ T$_1$cos(36.87°) - T$_2$cos(36.87°) + 0 = 0 (since the force of gravity has no affect on the x-component of the tensions, and the object is not accelerating).

⇔ T$_2$ = T$_1$cos(36.87°)/cos(36.87°) = T$_1$.

T$_1$$_y$+T$_2$$_y$+F$_g$$_y$=0.

⇔ T$_1$sin(36.87°) +T$_2$sin(36.87°)=F$_g$

⇔ 2T$_1$sin(36.87°)=F$_g$

Therefore,

⇔ T$_1$=.5kg(9.8m/(s2))/(2*sin(36.87°)) = 4.083N.

I've used up all but one of my attempts. Maybe it's because I'm not understanding the wording of the problem. I used up two attempts by guessing T$_1$+T$_2$ = 8.16/8.17 (I thought that it may be an issue with rounding).

Anyway, if someone could provide some input as to what the problem is asking, I would be extremely appreciative! And it would also be nice to have someone verify that my math and setup of this problem is correct. Thank you so much!

Last edited: Oct 9, 2012
2. Oct 9, 2012

ehild

I think you just miss a zero. It is 4.083 N

ehild

3. Oct 9, 2012

risepj

Whoops, I think I actually did use 4.083 when I submitted my answer. Later in my post you see that I said that T$_1$+T$_2$ equals 8.16/8.17, which is double 4.08.

Editing first post to reflect that.