Question #4c1d5

1 Answer
Mar 7, 2017

Answer:

(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.