- #1

tehmatriks

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## Homework Statement

A stone is projected vertically upwards from the ground with an initial velocity of 80 m s

^{-1}. Find the greatest height reached and the time taken. When will the stone be 96 m above the ground?

## Homework Equations

[v = u + at], [s = ut + ½at

^{2}], [v

^{2}= u

^{2}+ 2as]

*assume all falling objects have an acceleration of 9.8 m s*

^{-2}vertically downwards.## The Attempt at a Solution

*accerleration "a" = -9.8 m s*

initial velocity "u" = 80 m s

final velocity "v" = 0 m s

time "t" = ? s

^{-2}initial velocity "u" = 80 m s

^{-1}final velocity "v" = 0 m s

^{-1}time "t" = ? s

finding time "t" using

**v = u + at**

0 = 80 + (-9.8)t

t = 80/9.8

t = 8.16 s

finding greatest height i.e distance "s" using

**v**

^{2}= u^{2}+ 2as0

^{2}= 80

^{2}+ 2(-9.8)s

s = 80

^{2}/2(9.8)

s = 326.53

Now for the second bit, finding when the stone will be 96 m above the ground.