The acceleration is related to the force and mass by Newton's second law which states:
[tex]a=\frac{F}{m}[/tex]for the first mass we have:
[tex]a_1=\frac{5}{1}=5[/tex]If the same block is hit by a force of 40 N then the new acceleration is:
[tex]a=\frac{40}{1}=40[/tex]Which is eight times the original acceleration; therefore, the answer is D.