Physics equilibrium

[chiddler]

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I'm trying to find T1 and T2.

Given: m = 100 kg, Theta 1 = 30, Theta 2 = 60.

(Optional) What i'm doing for T2

I set vertical forces together and then horizontal.
Horz: T1cos(θ1) = T2 cos(θ2)
T1 = T2 cos(θ2) / cos(θ1)

Vert: mg = T1sin(θ1) + T2sin(θ2)
mg = (T2 cos(θ2) / cos(θ1)) + T2sin(θ2)
mg = T2 (cos(θ2) /cos(θ1) + sin(θ2)

T2 = 44.8

So i'm doing it wrong; answer is 50. Second of all, it's taking too much time with too many calculations!

halp!

 

[MedPR]

I'm trying to find T1 and T2.

Given: m = 100 kg, Theta 1 = 30, Theta 2 = 60.

(Optional) What i'm doing for T2

I set vertical forces together and then horizontal.
Horz: T1cos(θ1) = T2 cos(θ2)
T1 = T2 cos(θ2) / cos(θ1)

Vert: mg = T1sin(θ1) + T2sin(θ2)
mg = (T2 cos(θ2) / cos(θ1)) + T2sin(θ2)
mg = T2 (cos(θ2) /cos(θ1) + sin(θ2)

T2 = 44.8

So i'm doing it wrong; answer is 50. Second of all, it's taking too much time with too many calculations!

halp!

use something else to upload! imgur is blocked at my work computer.

 

[chiddler]

mmk

 

[ljc]

First off, there's no way the tension in either of those strings is only 50 when the mass is 100kg. 100kg = 1000N downward, so the combined tension in both strings must be at LEAST 1000N (will be exactly 1000N in the vertical, but in the diagnol will be more due to horizontal forces cancelling).

Secondly, in your work, when you substitute for T1 in the vertical, you drop the sin(01) term. That will mess up your calculations.

The answers I got were T1=500N, T2=865N

 

[MedPR]

I guess work computers block that second upload site too. If it's not solved by the time I go home I'll try to help.

MT Headed appears to be online though, so I anticipate a solution soon.

Edit: Unless ljc already solved it.

 

[chiddler]

First off, there's no way the tension in either of those strings is only 50 when the mass is 100kg. 100kg = 1000N downward, so the combined tension in both strings must be at LEAST 1000N (will be exactly 1000N in the vertical, but in the diagnol will be more due to horizontal forces cancelling).

Secondly, in your work, when you substitute for T1 in the vertical, you drop the sin(01) term. That will mess up your calculations.

The answers I got were T1=500N, T2=865N

Oops. The next question was 100kg. This one was supposed to be 10 kg.

Anyway, did you do the same thing I did or is there a shorter way to do this that i'm not seeing?

Minus the error of course.

 

[ljc]

In that case, it should be 50N and 86.5N (I believe, didn't re-do the work). Double check my work if you like, just to be safe. I'm tired.

Also, I don't think there are any shortcuts. I did exactly what you did. You just need to be confident going in so that you don't have to do the problem twice. Should be easy points as long as you don't mix anything up.

MedPR: It's a simple hanging mass system. Mass hangs from two strings which have angles of 30 and 60 (respectively) to the horizontal roof.

 

[chiddler]

In that case, it should be 50N and 86.5N (I believe, didn't re-do the work). Double check my work if you like, just to be safe. I'm tired.

Also, I don't think there are any shortcuts. I did exactly what you did. You just need to be confident going in so that you don't have to do the problem twice. Should be easy points as long as you don't mix anything up.

MedPR: It's a simple hanging mass system. Mass hangs from two strings which have angles of 30 and 60 (respectively) to the horizontal roof.

thanks for your help

thanks for trying to help medpr

 

[MT Headed]

I don't think there is a shorter way.

The mcat might have 1 or 2 questions this intense. Obviously you won't have time to solve more than that. They are testing to see if under a stressful timed scenario, can you correctly set up and solve the system the first time through, with no mistakes.

Since it is a multiple choice format, often you can guess the answer because the other three are obviously bad (like 50N 🙂 ) or have the wrong units (86.6kg). Or the angles will be something easier like 45 degrees.

Honestly this question is more homework-like and less MCAT-like.

 

[typicalindian]

What I would do is this:

In the Y direction you have
T1 sinθ1 + T2 Sinθ2 = mg

In the X direction you have
T2 cos θ2 - T1 cosθ1 = 0
I chose right as positive so thats why I picked T1 as being negative

Now I'm not going to go through the math but, in the X direction you should solve for T2 in terms of T1, then plug that in for T2 in the Y direction and use your algebra skills to solve T1

let me know if that helped

 

[MT Headed]

MedPR: It's a simple hanging mass system. Mass hangs from two strings which have angles of 30 and 60 (respectively) to the horizontal roof.

Actually it is a kinky picture with ropes and knots, and restraints on a really nice box. The image probably isn't safe for work anyways.

 

[MedPR]

I don't think there is a shorter way.

The mcat might have 1 or 2 questions this intense. Obviously you won't have time to solve more than that. They are testing to see if under a stressful timed scenario, can you correctly set up and solve the system the first time through, with no mistakes.

Since it is a multiple choice format, often you can guess the answer because the other three are obviously bad (like 50N 🙂 ) or have the wrong units (86.6kg). Or the angles will be something easier like 45 degrees.

Honestly this question is more homework-like and less MCAT-like.

That sucks. A lot of the time when I find myself doing a lot of work/math on a physics problem, I stop and reconsider my thought process. Even though physics is really tough for me right now, I try to remember that MCAT physics is supposed to be simple math, tough concept, not the other way around.

 

[MedPR]

MedPR: It's a simple hanging mass system. Mass hangs from two strings which have angles of 30 and 60 (respectively) to the horizontal roof.

Thanks. Going to look at this tonight, hopefully it makes sense.

Actually it is a kinky picture with ropes and knots, and restraints on a really nice box. The image probably isn't safe for work anyways.

One can only hope.

 

[dranet]

Some stuff on the MCAT has to be remembered like the sin and cos of angles 30, 45, 60, 90. Anyway Sin 30=.5 and sin 60= .84. You have to learn those! it definitely helps. The question calls for understanding of how to draw a vector diagram for the forcesand place terms into eqns like Typicalindian stated in his/her answer. It is a lot of maths for the MCAT but if this is a drill question to revise the basic calculations than its worthwhile to do.