Asked by shivanya
the distance travelled by an object thrown upwards in t seconds is 30t - 4.9t square metres. after how much time would it fall down? at what all times would it be 20 metres above the ground?
Answers
Answered by
Reiny
When it falls down, the distance is zero
so 0 = 30t - 4.9t^2
t(30 - 4.9t) = 0
t = 0 , that would be at the beginning
or
t = 30/4.9 or appr. 6.12 seconds
2nd part:
20 = 30t - 4.9t^2
4.9t^2 - 30t + 20 = 0
t = (30 ± √508)/9.8
= .761 seconds, on its way up
or
= 5.36 seconds, on the way down
so 0 = 30t - 4.9t^2
t(30 - 4.9t) = 0
t = 0 , that would be at the beginning
or
t = 30/4.9 or appr. 6.12 seconds
2nd part:
20 = 30t - 4.9t^2
4.9t^2 - 30t + 20 = 0
t = (30 ± √508)/9.8
= .761 seconds, on its way up
or
= 5.36 seconds, on the way down
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