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A ball is thrown upwards from a height of 16ms-1 from the edge of a cliff 144m above sea level. 
(Acceleration down wards = 9.8ms-2)

The displacement of the sea from the top of the cliff = -144m

Given that the displacement of the ball from the cliff top x seconds after it is throw upwards is x = 4.9x- 16x, prove that it will take 7.294 seconds for the ball to hit the sea. 
 

 Oct 18, 2020
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4.9x^2 - 16x = 144       

4.9x^2 - 16x - 144 = 0     use quadratic formula    a = 4.9    b= -16   c = -  144        x = 7.294  s      or  - 4.029 ( throw out)

 
 Oct 18, 2020

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