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# M1 tension string question watch

1. https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

In question 5b) I have worked out that B has travelled 0.3m but the mark scheme is 0.6m. Can anyone explain it as simple as possible. Long explanations are very confusing for me. Thanks.
2. Is it because the question is asking for distance travelled and you have calculated maximum displacement during the ballistic section of the motion.
3. I think you have worked out the distance that A travels from the moment B hits the plane and when A is at its maximum height. If you have, you have to double the distance because the point at which the string becomes taut again will be the position where A was when B hit the plane.
4. (Original post by nerak99)
Is it because the question is asking for distance travelled and you have calculated maximum displacement during the ballistic section of the motion.
Yes I did. Isn't that what the question is asking for though? The total distance. So when b moves downward, does a move? I thought a only starts to move after b hits the ground so the u of a would be the v of b... Thanks
5. (Original post by B_9710)
I think you have worked out the distance that A travels from the moment B hits the plane and when A is at its maximum height. If you have, you have to double the distance because the point at which the string becomes taut again will be the position where A was when B hit the plane.
I did exactly what you said which is working out the Max distance that a can reach. Do I have to take into account of the taut string in the question? I think I have misunderstood it. thanks.
6. (Original post by coconut64)
I did exactly what you said which is working out the Max distance that a can reach. Do I have to take into account of the taut string in the question? I think I have misunderstood it. thanks.
You have correctly worked out the max height of A. To get the 0.6m answer, you need to consider when the string will become taut again.
The string will be taut again when particle A comes back down to the same height that it was at when B hit the plane. So A will move 0.3m up, and then 0.3m down, back to the same position, and there will now be tension in the string - string is taut.
7. (Original post by B_9710)
You have correctly worked out the max height of A. To get the 0.6m answer, you need to consider when the string will become taut again.
The string will be taut again when particle A comes back down to the same height that it was at when B hit the plane. So A will move 0.3m up, and then 0.3m down, back to the same position, and there will now be tension in the string - string is taut.
Oh okay... I have got a few questions then
1) so a only starts to move when b hits the ground ( I have worked this out but not really sure why as surely they should move at the same time? )
2) what does it mean the the string is taut? Does it mean tension is the same
3) why will there be tension on the string again when a has travelled 0.6m ? Does it mean b has gone back up again? Thanks
8. They are both moving at the same time, but when there is tension in the string (the string is taut) the acceleration is the one that you calculated in the earlier part of the question. As soon as B hits the plane, the string is no longer taut and the only force now acting on A is weight - so it's acceleration is g - it's in free fall.
The question states that we assume B stays on the ground and does not get lifted at all.
9. (Original post by B_9710)
They are both moving at the same time, but when there is tension in the string (the string is taut) the acceleration is the one that you calculated in the earlier part of the question. As soon as B hits the plane, the string is no longer taut and the only force now acting on A is weight - so it's acceleration is g - it's in free fall.
The question states that we assume B stays on the ground and does not get lifted at all.
But why does a need to move back down then?
10. (Original post by coconut64)
But why does a need to move back down then?
For the string to be taut. A key point in the question is where it says something about the particle A not reaching the height of the pulley.

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