# Two blocks, one is hanging

1. Jul 2, 2008

### spidey12

Whoops, I know i made another post but i didnt realize i have another question that i left blank:

The weight of the block on a table is 452 N and that of the hanging block is 220 N. Ignore all frictional effects, and assuming the pulley to be massless.

What is Acceleration of the two blocks?

What is the tension?

2. Jul 2, 2008

### spidey12

So what i did was i tried to isolate the two Ns and i got seperate masses.

Then i did this: (452-220)/(46.1+22.4)

but that was wrong.

3. Jul 2, 2008

### rock.freak667

Assuming downward motion.

What is the resultant downward force on the hanging block?

and what would be the resultant force on the block on the table?

4. Jul 2, 2008

### spidey12

Is the force in the downward position simply 220 N?

5. Jul 2, 2008

### rock.freak667

There is tension,T, in the string acting upward. So the resultant downward force = (220-T)N

and if that block moves down, how does the other block move and what would be the resultant force on it?

6. Jul 2, 2008

### spidey12

if one block moves down the other moves to the left. the acceleration has to be the same since its a closed system. So the downward force is ma=220-T? what is "m"?

7. Jul 2, 2008

### rock.freak667

Yes

Correct

m is the mass of the 220N block. Depending on what you take 'g'. (W=mg)

8. Jul 2, 2008

### spidey12

Ok. So now what?

22.4a=220-T?

I dont know a or T

9. Jul 2, 2008

### rock.freak667

The other block moves to the left making Ma=T (where M is the mass of the 452N block)

10. Jul 2, 2008

### spidey12

So the correct equation is 22.4a=220-(ma of the other block)?

I'm getting so confused.

11. Jul 2, 2008

### spidey12

Ok os i reworked the problem and i got 3.39 as the acceleration is this correct?

12. Jul 2, 2008

### rock.freak667

Take one block at a time.

We know for the hanging one it's 22.4a=220-T

Now since the one on the table moves to the left and the only force on it is the tension,T, then the resultant force is Ma=T where M=mass of the 452N block.

solving them will give

22.4a=220-Ma

22.4a+Ma=220. Find a.

13. Jul 2, 2008

### rock.freak667

It is somewhere around 3, I got 3.21 using g=9.81 but I kinda did it in my head so it might be a bit off.

14. Jul 2, 2008

### spidey12

so the tension in the cord is simply the accelration of the system times the mass of the 452 N block?

15. Jul 2, 2008

### spidey12

3.39 was incorrect. I have 10 minutes left to submit this and no luck whatsoever :(

16. Jul 2, 2008

### spidey12

3.21 was correct, now the tension: T=mass of the 452 block * 3.21?

17. Jul 2, 2008

Yep.