The position of a body moving on a coordinate line is given by $\displaystyle s = \frac{9}{t^{2}}-\frac{3}{t}$ for $1 \leq t \leq 3$, with $s$ in meters and $t$ in seconds.

(a) Find the body's displacement and average velocity for the given time interval.
Displacement = $\mathrm{m}$
Average velocity = $\mathrm{m/s}$

(b) Find the body's velocity at the endpoints of the interval.
Velocity at $t = 1$ is $\mathrm{m/s}$
Velocity at $t = 3$ is $\mathrm{m/s}$

(c) Find the body's acceleration at the endpoints of the interval.
Acceleration at $t = 1$ is $\mathrm{m/s^2}$
Acceleration at $t = 3$ is $\mathrm{m/s^2}$

(d) When, if ever, during the interval does the body change direction? If there is more than one answer, enter a comma separated list. If the body never changes direction during the interval, enter NONE.
$t =$ $\mathrm{s}$