Two Blocks,joined by a String,have Masses of 3

Multiple Choice

Two blocks,joined by a string,have masses of 3.0 and 4.0 kg.They rest on a frictionless horizontal surface.A second string,attached only to the 4.0-kg block,has horizontal force = 40 N applied to it.Both blocks accelerate.Find the tension in the string between the blocks.

A) 23 N
B) 5.7 N
C) 17 N
D) 93 N
E) 120 N