Final answer:
Using Newton's second law, the acceleration caused by an 18.0 N force on a 3.0 kg mass is 6.0 m/s². The final velocity after 4.0 seconds is calculated to be 24.0 m/s using the kinematic equation v = u + at with an initial velocity of 0 m/s.
Step-by-step explanation:
To find the final velocity of a mass that was initially at rest, we can use Newton's second law and the kinematic equations. The force applied causes an acceleration, which is calculated by dividing the force by the mass (F/m=a). With the force of 18.0 N and mass of 3.0 kg, the acceleration is 6.0 m/s2. The kinematic equation v = u + at can be used to find the final velocity, where u is the initial velocity, a is the acceleration, and t is the time. Since the mass was initially at rest, u=0, the final velocity v after 4.0 seconds is (0 m/s) + (6.0 m/s2)(4.0 s) = 24.0 m/s.