A 4-Kg Mass and a 5-Kg Mass Are in Contact $2$

Multiple Choice

A 4-kg mass and a 5-kg mass are in contact with each other while resting on a smooth table. A 20-N external force is applied to the 5-kg mass (in a direction toward the 4-kg mass) . The acceleration of the 4-kg mass is

A) 1.8 m/s $2$
B) 3.1 m/s $2$
C) 2.2 m/s $2$
D) 3.8 m/s $2$