# Trouble with tensions and thrusts in towbars (M1)

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#1
First of all, I feel intensely stupid and thick-headed for having to post a question about M1 when I've been practising M3 all week, this is quite embarrassing.

In any case, my trouble lies with Q6 of June 2009 M1, Edexcel.

I can easily do part (a).

Part (b) was also pretty elementary, but I wasn't quite sure on the direction of the tension, how do you know that the tension is towards the car?

Part (c) is slightly more challenging. I don't quite understand what the markscheme did here. I'm assuming in the first part, it considers only the trailer, resolving away from the trailer to find the deceleration of the trailer, then the decelaration of the car should be the same, so you resolve away from the car, but I don't get how we get those forces from the resolving.

Edit: Oh, and why does the thrust in the towbar reverse direction from the tension? What is 'thrust'?
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5 years ago
#2
(Original post by Zacken)
First of all, I feel intensely stupid and thick-headed for having to post a question about M1 when I've been practising M3 all week, this is quite embarrassing.

In any case, my trouble lies with Q6 of June 2009 M1, Edexcel.

I can easily do part (a).

Part (b) was also pretty elementary, but I wasn't quite sure on the direction of the tension, how do you know that the tension is towards the car?

Edit: Oh, and why does the thrust in the towbar reverse direction from the tension? What is 'thrust'?
if you are not sure then choose at random tension or thrust ( which is the opposite of tension...the arrows point away from the centre of the rod ). if you make the wrong choice it will come out negative.
0
5 years ago
#3
(Original post by Zacken)
First of all, I feel intensely stupid and thick-headed for having to post a question about M1 when I've been practising M3 all week, this is quite embarrassing.

In any case, my trouble lies with Q6 of June 2009 M1, Edexcel.

I can easily do part (a).

Part (b) was also pretty elementary, but I wasn't quite sure on the direction of the tension, how do you know that the tension is towards the car?

Part (c) is slightly more challenging. I don't quite understand what the markscheme did here. I'm assuming in the first part, it considers only the trailer, resolving away from the trailer to find the deceleration of the trailer, then the decelaration of the car should be the same, so you resolve away from the car, but I don't get how we get those forces from the resolving.

Edit: Oh, and why does the thrust in the towbar reverse direction from the tension? What is 'thrust'?
In any coupling such as a towbar there is a force acting on the two coupled objects. If the force pulls it is called tension. If it pushes it is called thrust. Just assume it is always a tension in the coupling (unless otherwise stated or you are certain that it is a thrust) and if it is a thrust at the end of it all, then you get a negative answer. That is what we were taught to do in M1.
1
#4
(Original post by the bear)
if you are not sure then choose at random tension or thrust ( which is the opposite of tension...the arrows point away from the centre of the rod ). if you make the wrong choice it will come out negative.
(Original post by 16Characters....)
In any coupling such as a towbar there is a force acting on the two coupled objects. If the force pulls it is called tension. If it pushes it is called thrust. Just assume it is always a tension in the coupling (unless otherwise stated or you are certain that it is a thrust) and if it is a thrust at the end of it all, then you get a negative answer. That is what we were taught to do in M1.
Thanks! I was always scared to just choose one in case there working was more than just a 'come out negative' but you've re-assured me now!
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