The work done is 137 joules.
Lifting opposes the acceleration of gravity, which is 9.8 m/sec/sec.
20 x 0.7 x 9.8 = 137 J (kg-m2/sec2)
Fires in grasslands prevent the growth of shrubs. Plants can survive in these fires because most of them have parts underground, where fire cannot reach. Animals and runners aren't affected by this, because they can leave.
The isolation barriers prevents two of the species to mate, resulting in them evolving into different species