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    Help please!

    A pebble is projected vertically upwards with speed 21m/s from a point 32m above the ground.

    Find the total time for which the pebble is more than 40m above the ground

    Thanks
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    What have you done so far?
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    I have found the speed with which the pebble strikes the ground to be 33m/s (i.e. v)
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    (Original post by snoopyx)
    I have found the speed with which the pebble strikes the ground to be 33m/s (i.e. v)
    this is irrelevant.

    there is an equation for displacement in terms of u a and t correct?

    so you want to set this equal to 8. you'll get a quadratic in t with 2 roots, think about what this means in terms of the motion of the pebble.
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    (Original post by snoopyx)
    Help please!

    A pebble is projected vertically upwards with speed 21m/s from a point 32m above the ground.

    Find the total time for which the pebble is more than 40m above the ground

    Thanks
    Hint: Displacement
 
 
 
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Updated: July 19, 2009

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