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M1 thrust in tow bar Watch

1. hi, for part e ) of this question, I am a little confused about my answer compared to the markscheme s answer. Attachment 523405523407 the mark scheme has used the opposite direction which I don't get why. However their answer is positive as well but somehow they put a negative sign and changed it to positive. I got a positive value for mine by taking the right as my positive direction since the car is accelerating by -3/4. What is the difference? Thanks.
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2. (Original post by coconut64)
hi, for part e ) of this question, I am a little confused about my answer compared to the markscheme s answer. Attachment 523405523407 the mark scheme has used the opposite direction which I don't get why. However their answer is positive as well but somehow they put a negative sign and changed it to positive. I got a positive value for mine by taking the right as my positive direction since the car is accelerating by -3/4. What is the difference? Thanks.
if you mean the mini - sign to the top left of the T= 400N it looks like a typo
3. (Original post by thefatone)
if you mean the mini - sign to the top left of the T= 400N it looks like a typo
Are you sure? Why would they write it out twice then if that's the case? Thanks.
4. (Original post by coconut64)
hi, for part e ) of this question, I am a little confused about my answer compared to the markscheme s answer. Attachment 523405523407 the mark scheme has used the opposite direction which I don't get why. However their answer is positive as well but somehow they put a negative sign and changed it to positive. I got a positive value for mine by taking the right as my positive direction since the car is accelerating by -3/4. What is the difference? Thanks.
It doesn't matter which direction you take as positive.
Only reason I can see to take the direction they did, is the terms are then all positive.

PS. Sign to top left of the T is only a typo, in that it should have been a minus sign.

I presume they had T as tension, acting away from the car, then found it to be minus, and so is actually pushing the car.
5. (Original post by ghostwalker)
It doesn't matter which direction you take as positive.
Only reason I can see to take the direction they did, is the terms are then all positive.
Hi, I don't know what you mean by that because I took the right as the positive direction and that gives me a positive value as well. From their equation, the answer is also positive but I don't see the point of turning it to negative then back to positive if you get what I mean.. The final answer is positive...
6. (Original post by coconut64)
Are you sure? Why would they write it out twice then if that's the case? Thanks.
oh ok i see

so since they "guessed" the wrong direction for the force exerted on towbar thus the negative sign just means the force acts in the opposite direction to which the mark scheme defined positive in right?

Zacken is this right?
7. (Original post by coconut64)
Hi, I don't know what you mean by that because I took the right as the positive direction and that gives me a positive value as well. From their equation, the answer is also positive but I don't see the point of turning it to negative then back to positive if you get what I mean.. The final answer is positive...
No, from their equation the answer is -400

I presume they're using the same direction for T ss the first part of the question, and haven't changed things around. But you've not posted that, so just guessing.
8. (Original post by ghostwalker)
No, from their equation the answer is -400

I presume they're using the same direction for T ss the first part of the question, and haven't changed things around. But you've not posted that, so just guessing.
You are right sorry about that, I get what you mean now, it is the same thing it just that they have used a different direction, Thanks.
9. (Original post by thefatone)
oh ok i see

so since they "guessed" the wrong direction for the force exerted on towbar thus the negative sign just means the force acts in the opposite direction to which the mark scheme defined positive in right?

Zacken is this right?
Hi, don't worry about it, they have got a negative value so that's why they had to change it to a positive value at the end. Thanks.
10. (Original post by coconut64)
Hi, don't worry about it, they have got a negative value so that's why they had to change it to a positive value at the end. Thanks.
glad someone was able to help you to understand ^-^

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