At a 40 inch sid, where should the object be placed in relationship to the image receptor and x-ray source in order to make the object look twice as big? (i. e. mf = 2)

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. 

Density always stays the same no matter how much of the substance is present. density also expresses the proportional relationship between mass and volume of the substance.