from his playhouse, a child walks 11 m east, then 7 m north, then 13 m east. what is the direction of the child's displacement from his playhouse?

Ke reqd to move from 0 to 50 will be proportional to 50x50 or 2500. this is equal to w.  to change vel from 50 to 150 you need energy prop to 22500 - 2500 = 20,000. this corresponds to 8w.  best answer is a) . work reqd is prop to velocity squared. 

Answer is trees if this doesnt try using google