A 10 Kg Mass Hangs at the End of a Strong

Multiple Choice

A 1.0 kg mass hangs at the end of a strong, massless cord attached to a 2.0-kg mass. The 2.0-kg mass hangs at the end of another strong, massless cord. A force applied to the "upper" cord accelerates the system upward at 10 m/s². Assuming that the acceleration of gravity is 10 m/s², the tension in the lower cord is

A) 20 N.
B) 30 N.
C) 40 N.
D) 60 N.