What is the tension in the cord connecting the two blocks at this instant?

[huybinhs]

Homework Statement

The coefficient of static friction between block A and a horizontal floor is 0.45 and the coefficient of static friction between block B and the floor is 0.30. The mass of each block is 2.0 kg and they are connected together by a cord.

What is the tension in the cord connecting the two blocks at this instant?
Answer: N

Homework Equations

and

The Attempt at a Solution

as the friction force on the block A is 8.82 N, for just to move it the force is 8.82 N and this is applied by the cord only. Hence the tension in the cord is 8.82 N

T = 0.45 * 9.8 * 2 = 8.82 N => INCORRECT. Why? Please help!

 

[tiny-tim]

Hi huybinhs!

At what instant? You haven't said what is happening to the blocks.

 

[huybinhs]

Hi huybinhs!

At what instant? You haven't said what is happening to the blocks.

Part a for this problem is "If a horizontal force F pulling on block B is slowly increased until it is barely enough to make the two blocks start moving, what is the magnitude of F at the instant they start to slide?"

I already figured it out that the answer is 15.092 N.

I don't know how to do part 2. Please help!

 

[tiny-tim]

Part a for this problem is "If a horizontal force F pulling on block B is slowly increased until it is barely enough to make the two blocks start moving, what is the magnitude of F at the instant they start to slide?"

ahhh!

ok then, the acceleration of the second block is zero, so just balance the forces on the second block.

(or the first block … same result … just takes a bit longer )

 

[huybinhs]

Ok. Thanks! My answer is CORRECT, my instructor just fixed it. Thanks anyway ;)