You are Here: Home >< Maths

1. Can someone please help for part c only? I have got the acceleration wrong as it is meant to be -1/30. My working out is below - would really appreciate if someone can show me what has went wrong with my working out.

Attachment 725058725060
Attached Images

2. Part a) the calculation is -400/12000=a
a=-1/30
3. (Original post by Howie_2114)
Part a) the calculation is -400/12000=a
a=-1/30
Thanks but what has went wrong in my working out?
4. F=-150-250=-400
a=F/m
a= -400/12000=-1/30
The 150 and 250 are going in the same direction, and your
5. And you take positive going in the opposite direction as the 400N is the resisting(stopping) the barge moving
6. i hope this helps
7. (Original post by Howie_2114)
And you take positive going in the opposite direction as the 400N is the resisting(stopping) the barge moving
Thanks so much
But I thought you can choose your positive direction?
Also, the canal barge is moving to the left since nicholas is pulling the rope and pat is leaving his rope slack.
And how come the resistance 250N is in the same direction as the 150n tension? Since the canal barge is moving to the left, then surely the resistance is in the other direction?

Edit: so sorry I meant to say since the canal barge is moving to the left
8. (Original post by sienna2266)
Thanks so much
But I thought you can choose your positive direction?
Also, the canal barge is moving to the right since nicholas is pulling the rope and pat is leaving his rope slack.
And how come the resistance 250N is in the same direction as the 150n tension? Since the canal barge is moving to the right, then surely the resistance is in the other direction?
Yes you can choose your +ve dir. You chose it to be to the LEFT.

The barge is moving to the RIGHT and when Pat makes it rope slack the barge begins to decelerate so that it is still moving to the RIGHT (hence the resistive force is still to the LEFT until it comes to rest). Also Nicholas is adding on a force to the left with his rope, hence the eq of motion is and hence .
It is not negative since in the mark scheme they probably took the standard approach of taking RIGHT as the +ve direction, so that the eq of motion becomes
9. (Original post by RDKGames)
Yes you can choose your +ve dir. You chose it to be to the LEFT.

The barge is moving to the RIGHT and when Pat makes it rope slack the barge begins to decelerate so that it is still moving to the RIGHT (hence the resistive force is still to the LEFT until it comes to rest). Also Nicholas is adding on a force to the left with his rope, hence the eq of motion is and hence .
It is not negative since in the mark scheme they probably took the standard approach of taking RIGHT as the +ve direction, so that the eq of motion becomes
Thanks so much! But why doesn't the barge move backwards when Nicholas pulls on it and Pat leaves her rope slack? How does it not move backwards and instead just end up decelerating in the direction it was going initially? I was assuming that the pull on the rope exerted by nicholas is strong enough to pull the barge to the left, changing its direction of motion.
10. (Original post by sienna2266)
Thanks so much! But why doesn't the barge move backwards when Nicholas pulls on it and Pat leaves her rope slack? How does it not move backwards and instead just end up decelerating in the direction it was going initially? I was assuming that the pull on the rope exerted by nicholas is strong enough to pull the barge to the left, changing its direction of motion.
I'm not sure how to explain the "why" as it should be fairly obvious and intuitive. Pat pulls so that the barge is moving to the right and builds up its speed, then after it moves 10m Pat lets go and Nicholas picks it up from the other side. The barge must first come to rest before it is moving to the left and it surely doesn't come to rest as soon as Nicholas starts pulling it.
11. [QUOTE=sienna2266;76120544]Can someone please help for part c only? I have got the acceleration wrong as it is meant to be -1/30. My working out is below - would really appreciate if someone can show me what has went wrong with my working out.

What u did was say water resistance and nicholas pulling is happening in different directions when its not, its happening in the same direction.

Pat let go of the rope but its still moving forwards

water resistance is slowing it down as well as nicholas pulling it from behind to help slow it down.

So the two forces need to be in the same direction
12. (Original post by RDKGames)
I'm not sure how to explain the "why" as it should be fairly obvious and intuitive. Pat pulls so that the barge is moving to the right and builds up its speed, then after it moves 10m Pat lets go and Nicholas picks it up from the other side. The barge must first come to rest before it is moving to the left and it surely doesn't come to rest as soon as Nicholas starts pulling it.
Thank you very much -managed to complete the question
13. (Original post by BlobBlob69)

What u did was say water resistance and nicholas pulling is happening in different directions when its not, its happening in the same direction.

Pat let go of the rope but its still moving forwards

water resistance is slowing it down as well as nicholas pulling it from behind to help slow it down.

So the two forces need to be in the same direction
Thank you

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 15, 2018
The home of Results and Clearing

### 2,961

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. SAE Institute
Animation, Audio, Film, Games, Music, Business, Web Further education
Thu, 16 Aug '18
2. Bournemouth University
Fri, 17 Aug '18
3. University of Bolton
Fri, 17 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams