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    This type of question comes up a lot but I never know how to answer it and don't really understand the mark scheme

    Part b)

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    (Original post by G.Y)
    This type of question comes up a lot but I never know how to answer it and don't really understand the mark scheme

    Part b)

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    If the particle is traveling due north then that means its velocity vector must be pointing due north. So the velocity will be 0i + kj i.e. it has no i component.

    Does that help? If not, please post what equations you already have.
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    (Original post by Notnek)
    If the particle is traveling due north then that means its velocity vector must be pointing due north. So the velocity will be 0i + kj i.e. it has no i component.

    Does that help? If not, please post what equations you already have.
    Okay but how do I go about finding the j component?

    I'm trying to use a suvat to work it out but the only known values that can be used are u and a
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    (Original post by G.Y)
    Okay but how do I go about finding the j component?

    I'm trying to use a suvat to work it out but the only known values that can be used are u and a
    You can use v = u + at like you did in a) but with an unknown t. This will give you a vector with i and j components in terms of t.

    Set the i component to 0 to give the time that the velocity is due north then use that to write down the velocity vector at this time.
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    since the acceleration is constant you can apply the SUVAT equations if you want.
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    (Original post by Notnek)
    You can use v = u + at like you did in a) but with an unknown t. This will give you a vector with i and j components in terms of t.

    Set the i component to 0 to give the time that the velocity is due north then use that to write down the velocity vector at this time.
    v = -2j + 2i + (0.25i + 0.3j)t

    i = 0

    v = -2j + 0.3jt

    v is still an unknown multiple of j so how do you get the time?
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    (Original post by G.Y)
    v = -2j + 2i + (0.25i + 0.3j)t

    i = 0

    v = -2j + 0.3jt

    v is still an unknown multiple of j so how do you get the time?
    It's not that i = 0 because this doesn't make sense since i is a unit vector which is not 0. The i component is equal to 0.

    v = -2j + 2i + (0.25i + 0.3j)t

    You can rewrite this

    v = (2 + 0.25t)i + (-2 + 0.3t)j

    Now set the i component to 0 to find the value of t.
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    (Original post by Notnek)
    It's not that i = 0 because this doesn't make sense since i is a unit vector which is not 0. The i component is equal to 0.

    v = -2j + 2i + (0.25i + 0.3j)t

    You can rewrite this

    v = (2 + 0.25t)i + (-2 + 0.3t)j

    Now set the i component to 0 to find the value of t.
    Oh

    2 + 0.25t = 0
    t = -8

    Do I just ignore the minus and say t=8 since time can't be negative?
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    (Original post by G.Y)
    Oh

    2 + 0.25t = 0
    t = -8

    Do I just ignore the minus and say t=8 since time can't be negative?
    You made a mistake in this line which I copied to my post without checking:

    v = -2j + 2i + (0.25i + 0.3j)t

    It should be -2i + 2j instead of -2j + 2i.
 
 
 
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