Question

Question #4c1d5

Answer 1

(Approximately) `91.3` km/h

Explanation:

We are told
`color(white)("XXX")80=0.0081s^2+0.137s`

written in standard parabolic form:
`color(white)("XXX")0.0081s^2+0.137s-80=0`

using the quadratic formula for solutions:
`color(white)("XXX")s= (-0.137+-sqrt(0.137^2-4 xx 0.0081 xx (-80)))/(2 xx 0.137)`

with the help of a spreadsheet to do the calculations:
`color(white)("XXX")s=91.28317433color(white)("XX")orcolor(white)("XX")s=-108.1967546`
and we can ignore the negative result as extraneous.