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## Homework Statement

A stone is flung straight up from a point 1.50 m above the ground and with an initial speed of 19.6 m/s.

a. What is the stone's maximum height above the ground?

b. How much time passes before the stone hits the ground?

## Homework Equations

The four kinematic equations

## The Attempt at a Solution

I used the kinematic equation: x=1/2(v+vo)t, solved for t, and got 2 s. (I used x=21.1, v=0, and vf=19.6). The answer book used x=xo+vot+1/2at^2, and got 4.08 s.

My REAL questions are:

1)why is it better to use the equation they did?

2)shouldn't all of the kinematic equations given the same answer? Does it have to do with the eqn I used had velocity, while theirs had distance?