Answer
$t = 100~min$
Work Step by Step
In part (a), we found that the rotational kinetic energy of the flywheel is $4.9\times 10^7~J$
We can find the time the truck can operate on the energy stored in the flywheel:
$t = \frac{E}{P}$
$t = \frac{4.9\times 10^7~J}{8.0\times 10^3~W}$
$t = 6125~s$
$t = 100~min$
