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    If a question details that a ball is thrown into the air from a height of, for example, 2.3m and I had to work out how long it takes to hit the ground, would s (displacement) = -2.3 because it's ending up -2.3m from it's starting point?

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    yes.
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    first : U put the direction of +ve and -ve... so assuming that u chose -ve to be downward:
    so the ball is moving DOWNWARD ==> S is -ve
    if its initial velocity is UPWARD ==> it's +ve
    as acceleration is DOWNWARD ==> it's -g

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    (Original post by chewwy)
    yes.
    no it's not yes!
    u can assume downward to be +ve and upward to be -ve: hence s would be +ve.
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    (Original post by yazan_l)
    no it's not yes!
    u can assume downward to be +ve and upward to be -ve: hence s would be +ve.
    You could. But there'd be no point.
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    (Original post by Libertine)
    You could. But there'd be no point.
    r u sure?
    take this:
    a ball is thrown downwards with initial velocity 20ms-1 from 100m. find after how long it will hit the ground.

    why would u use -ve in that question? why not assume downwards to be +ve? which is easier to deal with.
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    (Original post by yazan_l)
    r u sure?
    take this:
    a ball is thrown downwards with initial velocity 20ms-1 from 100m. find after how long it will hit the ground.

    why would u use -ve in that question? why not assume downwards to be +ve? which is easier to deal with.
    Okay point taken, but I was talking about this case where it was thrown upwards. And I would probably still use up as positive in your question because I find it less confusing to always do stuff the same way round.
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    well... all what i was saying is that it doesnt always have to be that way... whether displacement is +ve or -ve is something that U put. it might be easier to do stuff the same way round,,, but in further levels it would be much easier to put the directions in the way that the question is easier to do.
    so my point is that DEPENDING on YOUR assumtion u put the sign of each magnitude.
 
 
 
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Updated: November 23, 2005

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