Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta

[Mechanics] Confused with problem involving thrust watch

    • Thread Starter
    Offline

    11
    ReputationRep:
    Attachment 701274
    I’ve done a) b) of this question, where I had to show Acceleration was 0.75 and find the tension in tow bar.

    Is there anything wrong with the following diagram? I’m pretty sure that the thrust is pushing the 2 objects inside (together).
    Name:  9C108FE1-5590-4D63-AFC7-F4E390C9560A.jpg
Views: 68
Size:  245.4 KB

    I am unsure what the solution of F + 200 - 100 = 900a means (particularly why I have to subtract 100N. I think it’s the thrust but I don’t know how it’s acting on the car).
    Offline

    11
    ReputationRep:
    (Original post by FuryBall)
    Attachment 701274
    I’ve done a) b) of this question, where I had to show Acceleration was 0.75 and find the tension in tow bar.

    Is there anything wrong with the following diagram? I’m pretty sure that the thrust is pushing the 2 objects inside (together).
    Name:  9C108FE1-5590-4D63-AFC7-F4E390C9560A.jpg
Views: 68
Size:  245.4 KB

    I am unsure what the solution of F + 200 - 100 = 900a means (particularly why I have to subtract 100N. I think it’s the thrust but I don’t know how it’s acting on the car).
    i cant see the attachement
    • Thread Starter
    Offline

    11
    ReputationRep:
    Name:  6B2F18C9-DC30-42B0-9BFC-6975149FE966.jpg
Views: 54
Size:  351.3 KB
    (Original post by Onlineslayer)
    i cant see the attachement
    I also realized that the second diagram I drew is incorrect in terms of direction of tension.
    Offline

    11
    ReputationRep:
    (Original post by FuryBall)
    Attachment 701274
    I’ve done a) b) of this question, where I had to show Acceleration was 0.75 and find the tension in tow bar.

    Is there anything wrong with the following diagram? I’m pretty sure that the thrust is pushing the 2 objects inside (together).
    Name:  9C108FE1-5590-4D63-AFC7-F4E390C9560A.jpg
Views: 68
Size:  245.4 KB

    I am unsure what the solution of F + 200 - 100 = 900a means (particularly why I have to subtract 100N. I think it’s the thrust but I don’t know how it’s acting on the car).
    Great. Do not think too deep about this.

    Now, to help your understanding better, try to draw two separate diagram of forces for each vehicle.

    Thrust is a push force from the car, it is opposite to a pull force (tension). So if you look at your solution to (a) and (b), those two little arrows facing each other were tension forces. In (c) however, the thrust would be two little arrows facing away from each other.

    What I mean is, the Thrust force is pointing toward the right of the trailer, and pointing towards the left of the car.

    So, for the trailer: The trailer has two forces acting on it, The 100N usual resistance and the 100N thrust both acting towards the right hand side. therefore deceleration is:

    a = (100N + 100N)/300kg = 2/3


    As for the car, there are three forces acting on it, the Thrust on the car is now acting towards the left (as I said earlier), The brake force F is towards the Right, The 200N resistance is also towards the right.
    Hence:
    F + 200 - 100 = 900a

    where a=2/3

    You do not need to worry about the forces acting on the trailer at this point, because as far as the car is concerned, these are the only forces acting on it. (as you can see from the forces diagram I told you to draw separately).

    However, if you must know why we have done so, it is simply because if we wanted to include every force in the diagram, then we could have just had
    F + 200 - Thrust + Thrust + 100N = 900a + 300a
    and we will get exactly same result because a=2/3
    LOL
    Offline

    11
    ReputationRep:
    (Original post by FuryBall)
    Name:  6B2F18C9-DC30-42B0-9BFC-6975149FE966.jpg
Views: 54
Size:  351.3 KB
    I also realized that the second diagram I drew is incorrect in terms of direction of tension.
    , Nah, that was Thrust, and so the directions was very correct.
    • Thread Starter
    Offline

    11
    ReputationRep:
    Thanks for the reply. Yes I understand it now. Why did you write “LOL”? hahah
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    11
    ReputationRep:
    (Original post by FuryBall)
    Thanks for the reply. Yes I understand it now. Why did you write “LOL”? hahah
    hahaha don't mind me, I tend to be very unserious sometimes. And how come you have been awake all through. I actually went to bed and later woke up to solve it.
    • Thread Starter
    Offline

    11
    ReputationRep:
    Different time zones haha.
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    11
    ReputationRep:
    (Original post by FuryBall)
    Different time zones haha.
    true, you live in Japan
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by Onlineslayer)
    true, you live in Japan
    How could you tell!
    Offline

    11
    ReputationRep:
    (Original post by FuryBall)
    How could you tell!
    'Cause I am creepy. Just kidding. Let's just say I did my research.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: November 5, 2017
Poll
Do you like carrot cake?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.