Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    5
    ReputationRep:
    Name:  IMG_4479[1].jpg
Views: 42
Size:  523.5 KBneed help on Q18 all parts, is it simultaneous eq's? Thanks
    • Study Helper
    Online

    13
    Study Helper
    (Original post by Sniperdon227)
    Name:  IMG_4479[1].jpg
Views: 42
Size:  523.5 KBneed help on Q18 all parts, is it simultaneous eq's? Thanks
    Not as such.

    a) You should be able to do.

    b) reset the clock so that t=0 when B starts, and now work out s (displacement for A and for B). When they meet, they're equal, so equate and solve for t.
    Displacement for A needs a bit of thought - post your initial equation/thoughts, if in doubt.


    c) Knowing t, you can find the velocities.

    Edit: B_9710 has given a slightly different, more standard, method below, so be clear to whom you're replying, if you do.
    Offline

    15
    ReputationRep:
    Just use the SUVAT equations to find the distance in terms of t, and then equate the 2. remember though, for the car B, it is initially 5 seconds behind, so replace t with (t-5) when you find an expression for the distance that B has travelled after t seconds. (Because when t=5 A has moved but B hasn't).
    Offline

    15
    ReputationRep:
    Actually, looking at it there are probably better ways of doing this.
    • Thread Starter
    Offline

    5
    ReputationRep:
    The answers are a)25 b)20seconds
    Okay when I used; s= ut +0.5a(t)^2 where
    A)
    s=
    u=0
    v=
    a=2
    t=(t+5)

    B)s=
    u=0
    v=
    a=3.125
    t=t

    it worked however when I did what B_9710 said it never worked A(let t=t) B(let t=(t-5))
    Offline

    15
    ReputationRep:
    (Original post by Sniperdon227)
    The answers are a)25 b)20seconds
    Okay when I used; s= ut +0.5a(t)^2 where
    A)
    s=
    u=0
    v=
    a=2
    t=(t+5)

    B)s=
    u=0
    v=
    a=3.125
    t=t

    it worked however when I did what B_9710 said it never worked A(let t=t) B(let t=(t-5))
    You have to take great care doing it the way I suggested which is why I said that other ways are probably a bit easier.
    • Study Helper
    Online

    13
    Study Helper
    (Original post by Sniperdon227)
    it worked however when I did what B_9710 said it never worked A(let t=t) B(let t=(t-5))
    With B_9710's method it works fine, but you get t=25. Since you've used t as the time for A, then it's 25 seconds after A started, which makes it 20 seconds after B started - the desired result.
    • Thread Starter
    Offline

    5
    ReputationRep:
    (Original post by ghostwalker)
    With B_9710's method it works fine, but you get t=25. Since you've used t as the time for A, then it's 25 seconds after A started, which makes it 20 seconds after B started - the desired result.
    I get it the answer in each case needs interpreting, thanks for your help guys
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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