In 2014 the Philae spacecraft became the first artifact to land on
a comet. Unfortunately, Philae bounced off the comet's surface
and ultimately landed in a nonideal location. After its first contact,
Philae was moving upward at 38 cm/s, and it rose to a maximum
height of about 1 km. Estimate the gravitational acceleration of the
comet, assuming it's constant (not a very good assumption in this
case).