# M1 revision problemWatch

This discussion is closed.
#1
I find M1 okay generally but when it comes to questions such as;
- State how you have used the information that the string is inextensible.
- Explain briefly where the assumption that the strings are light has been used in your answer to part (a).

I really stumble. Can anyone tell me what common mistakes are?
I answer these questions and my teacher gives me 1/2 marks because he said I am along the right lines but I'm missing things out. Is there a technique to answering these questions?
0
14 years ago
#2
If you learn the properties of (say) a light inextensible string, and start by quoting those

so light that mass can be neglected.
no stretching, so length remains same whatever value of T, or whatever motion there is.

you should then have a better chance of perceiving the consequences of these properties for the question.

Aitch
0
14 years ago
#3
OK say that there is an object connected to a string and there is a xN force pulling on the string, and you have to find the force exerted on the object, you will resolve the tension etc. so hence you have assumed that the string is inextensible since if it was extensible then some of that force would be used to stretch the string. Then if there is another question and you have to find moments or something (for example), and in the system there are strings, you dont consider the weight of the strings. Hence you have assumed that the strings are light.

Now do you understand where you would write that?
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