Pan A

A web page designer creates an animation in which a dot on a computer screen has position

$F=[4\mathrm{.}0(cm)+(2\mathrm{.}5\frac{cm}{s^2})t^2]i+(5\mathrm{.}0c\frac{m}{s})tj$

Find the magnitude of the dot's average velocity between $t=0$ and $t=20s$ Express your answer with the appropriate units.