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# Mechanics 1 Help - finding mass of a weight on a pulley Watch

1. I'm doing some past papers in preparation for my summer exams. I've come across a question which is asking for me to do something I haven't been taught in class nor is it in my revision guide.

The question is:

4) Two particles A and B are connected by a light inextensible string which passes over a smooth fixed pulley. A has mass 4kg and descends 2.8m in the first 2 seconds. after the system us released from rest, the hanging parts of the string being vertical. Find the mass of B and tension in the string.

I've labelled mass B as 'mkg', which I have come across in previous questions, where it has asked me to find the acceleration instead of the mass. I know how to work out the tension, though I won't be able to do this until I know some more of the values.

Thanks!
2. (Original post by rodstagraam)
I'm doing some past papers in preparation for my summer exams. I've come across a question which is asking for me to do something I haven't been taught in class nor is it in my revision guide.

The question is:

4) Two particles A and B are connected by a light inextensible string which passes over a smooth fixed pulley. A has mass 4kg and descends 2.8m in the first 2 seconds. after the system us released from rest, the hanging parts of the string being vertical. Find the mass of B and tension in the string.

I've labelled mass B as 'mkg', which I have come across in previous questions, where it has asked me to find the acceleration instead of the mass. I know how to work out the tension, though I won't be able to do this until I know some more of the values.

Thanks!
use suvat equations to work out the acceleration
3. (Original post by gdunne42)
use suvat equations to work out the acceleration
that seems quite obvious. thanks!
4. (Original post by rodstagraam)
that seems quite obvious. thanks!
Yep if it's a question that you know is usually all about forces / acceleration and they tell you stuff about distances and times or velocities then there's going to be a bit of suvat in the solution.
5. Here's my answer, I think it's right, but don't take my word on it, as it's been many months since I've done M1.

6. was it right? just out of pure curiosity?
7. (Original post by paulpaulpauln)
was it right? just out of pure curiosity?
I think you may have made an error solving your simultaneous equations

By adding them together to eliminate T I get

4g - mg = 5.6 + 1.4m

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