Mechanics - Springs and pulleys

cupid.callin · Mar 25, 2011

Homework Statement

Diagram of a frictionless massless pulley with a 7 kg block and a 6 kg block hanging on either side, each attached to a spring of constant K = 10 N/m, and a 5 kg block and a 4 kg block below the springs, with a string tied to the ground beneath the 4 kg block.

The Attempt at a Solution

I could say that (A)(B) are correct and (C) is wrong and i know 4kg block will have acceleration but i don't know how to find it.

Doc Al · Mar 25, 2011

Hint: What's the tension in the spring connected to the 4kg block?

cupid.callin · Mar 25, 2011

Doc Al said:

Hint: What's the tension in the spring connected to the 4kg block?

Hi Doc Al
thanks for replying

I know i need to find kx to find acceleration

so initially kx = mg + T

and even if i apply Newton laws to rest of the blocks ... i can't find the extension

Doc Al · Mar 25, 2011

Start by analyzing the forces on the 6 kg block.

cupid.callin · Mar 25, 2011

ok ...

let tension in upper string is T₁ and string with 4kg is T₂
and extension in left and right spring is x₁ and x₂

Handwritten working on lined paper: 4kg: kx2 = 4g + T2; 6kg: T1 = 6g + kx2; 7kg: T1 = 7g + kx1; 8kg: kx1 = 5g; then T1 = 5g + 7g = 12g; kx2 = 6g, 12g - 6g = 6g; 4a = kx2 - 4g = 6g - 4g = 2g; a = 5.

OH MY GOD

DOC AL ... YOU ARE MY HERO !

And just one more question ,,, (just out of curiosity) ... what does AL means in Doc Al

Doc Al · Mar 25, 2011

cupid.callin said:

And just one more question ,,, (just out of curiosity) ... what does AL means in Doc Al

It's my name. Clever, eh?

cupid.callin · Mar 25, 2011

Doc Al said:

It's my name. Clever, eh?

And congrats ... you're going to reach 30,000 posts soon ... i guess maximum till now

Mechanics - Springs and pulleys

Homework Statement

The Attempt at a Solution

Discussion

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