Finding the speed before impact using the work-energy theorem

[tiffannielee]

Homework Statement

A blue whale materializes 11.5 km above an airless planet with an acceleration of gravity of 6.85 m/s². What is the speed of the whale right before impact? Use the work energy theorem.

Homework Equations

Work energy theorem : W = the change in k
W=k_f - k_o
w=1/2(mv_f²) - 1/2(mv_o²)

 

[Doc Al]

So what force acts on the whale? How much work is done by that force as the whale falls to the surface?