Mastering physics :pulleys and friction

[madah12]

Homework Statement

http://img7.imageshack.us/img7/8717/friction.png

Homework Equations

The Attempt at a Solution

T-W_a=0
W=mg=-186.6
T=186.6
T-Q-fs=0
186.6-Q-fs

fs=uN
N=60+147=207
fs=82.8
186.6-Q-82.8=0
Q=103.8
what is wrong??

 

[Doc Al]

Note: They want the maximum value of Q.

 

[madah12]

wait so should I take the direction of friction to the right? 82.8+186.2=269 .. but that also isn't in the choice list

Edit: wait I have things to two significant figures right? so is 270 the right answer?

 

[Doc Al]

wait so should I take the direction of friction to the right? 82.8+186.2=269 .. but that also isn't in the choice list

Edit: wait I have things to two significant figures right? so is 270 the right answer?

Yes.

 

[rwisz]

Hello,

Thank you for sharing your attempt at the solution to this problem. It appears that you have correctly identified the forces acting on the system (tension, weight, normal force, and friction) and have set up the equations correctly. However, there may be a few errors in your calculations.

Firstly, it seems that you have used the incorrect value for the weight of the block. The image shows the weight to be 147 N, not -186.6 N. This may have resulted in some discrepancies in your final answer.

Additionally, it is important to note that the coefficient of friction, u, is not given in the problem. Without this information, it is difficult to accurately calculate the value of friction. It is possible that this is the reason for the discrepancy in your final answer.

It may also be helpful to double check your signs in the equations. For example, the tension T should be equal to the weight W minus the applied force W_a, so it should be T = W - W_a, not T - W_a = 0 as you have written.

Overall, it seems that your approach to the problem is correct, but there may be some errors in your calculations. I would suggest reviewing the given information and equations, and double checking your calculations to see if you can identify where the error may have occurred. Additionally, if you are still having trouble, it may be helpful to seek assistance from a teacher or classmate.

Best of luck in solving this problem!