Hard physics question

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    Can anyone help with this please:
    A pebble is dropped from a height level with the end of a diving board above a lake. The velocity of the pebble immediately before it hits the surface of the water is 12m/s. Calculate the height of the diving board.

    The only answer i can think of is 12 (Got that by getting time as 1 second)
    but I don't think that's right.
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    (Original post by LittleBoxes)
    Can anyone help with this please:
    A pebble is dropped from a height level with the end of a diving board above a lake. The velocity of the pebble immediately before it hits the surface of the water is 12m/s. Calculate the height of the diving board.

    The only answer i can think of is 12 (Got that by getting time as 1 second)
    but I don't think that's right.
    7.3m

    use v^2 = u^2 + 2as

    btw the answer will be different depending on your value of g. I used g = 9.81
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    first step a little diagram.
    mark your positive direction
    mark distance as x or s (whatever you are used to using)
    a=9.81ms or -9.81ms depending on your diagram
    u=0m/s v=12m/s

    do a suvat

    t is missing

    so I think we use v^2=u^2+2as

    you have to do a suvat, you have to have a little cheat sheet with you until you memorise all the equations of motion. You might be given them on the formula sheet.
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    Isn't it just v^2 = u^2 +2as.
    Where v = 0's^-1
    u = -12 ms^-1
    a = -9.8ms^-1


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    (Original post by KINGYusuf)
    7.3m

    use v^2 = u^2 + 2as

    btw the answer will be different depending on your value of g. I used g = 9.81
    (Original post by KINGYusuf)
    7.3m

    use v^2 = u^2 + 2as

    btw the answer will be different depending on your value of g. I used g = 9.81
    (Original post by flux capacitor)
    first step a little diagram.
    mark your positive direction
    mark distance as x or s (whatever you are used to using)
    a=9.81ms or -9.81ms depending on your diagram
    u=0m/s v=12m/s

    do a suvat

    t is missing

    so I think we use v^2=u^2+2as

    you have to do a suvat, you have to have a little cheat sheet with you until you memorise all the equations of motion. You might be given them on the formula sheet.
    (Original post by RossB1702)
    Isn't it just v^2 = u^2 +2as.
    Where v = 0's^-1
    u = -12 ms^-1
    a = -9.8ms^-1


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    Yes, thanks so much, I get it now. Anyone know how to answer this:
    A journalist is deciding whether to walk, cycle, or take the bus to get to work. There are two routes he could take.The shorter route is along a 3.5km path that only pedestrians and cyclists are allowed to use. The bus takes a longer route along a road. Estimate how long it would take the journalist to walk the pedestrian route.
    I have no idea, why have they given only distance?
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    as it's an estimate question I think you need to know or give a good guess for the speed of a person walking. With this piece of info you can then work out the time. (5km/h)
 
 
 
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