# If an object with uniform acceleration (or deceleration) has a speed of 4 m/s at t=0 and moves a total of 8 m by t=4, what was the object's rate of acceleration?

Dec 11, 2015

I found a deceleration of $- 1.0 \frac{m}{s} ^ 2$

#### Explanation:

We can try to use:
${x}_{f} - {x}_{i} = {v}_{i} t + \frac{1}{2} a {t}^{2}$
with:
${x}_{f} - {x}_{i} = 8 m$
$t = 4 s$ (I think)
${v}_{i} = 4 \frac{m}{s}$
to get:
$8 = 4 \cdot 4 + \frac{1}{2} a {\left(4\right)}^{2}$
$8 = 16 + 8 a$
$a = - \frac{8}{8} = - 1.0 \frac{m}{s} ^ 2$