Pulley + spring balance problem.

[Lexadis]

Homework Statement

A light spring passing over a smooth pulley carries a spring balance of mass 1 kg and two weights of masses 1 kg and 2 kg. the reading on the balance will be

Homework Equations

3. The Attempt at a Solution [/B]
to my knowledge whatever the tension above the spring balance the reading will not change, it is only affected by the reading below it. Therefore I considered
reading = weight of spring balance + 1N
Reading = 20N
But I'm not sure whether this is the right approach. Should the mass of spring be considered? Or will there be some sort of acceleration taking place?

Thank you.

 

[BvU]

Hi,

You want to draw a free body diagram of the spring balance.

Is your 1 N a typo? DId you mean 10 N ?

To help you form an idea of the situation:

Suppose the spring balance + 1kg weight hangs from a nail in the wall.
What does the balance reading show ?
What is the force on the nail ?​

 

[Lexadis]

It was 10 N ^^
So.. It would look like this: (attachment)
Therefore, reading = 10N
Would that be okay?
Thank you

 

[BvU]

I think I agree.
Just for fun: what would the reading be if the spring balance were turned upside down ?

 

[Lexadis]

20N?
I'm not very sure though..

 

[BvU]

I agree - again !
I suppose the only way to be really sure is to do the experiment...

 

[Lexadis]

True :D
Thank you very much :)