Find the magnitude of that force

A nucleus that captures a stray neutron [in a nuclear reactor, for example] must bring the neutron to a stop within the diameter of the nucleus by means of the strong force.That force, which “glues” the nucleus together, is approximately zero outside the nucleus. Suppose that a stray neutron with an initial speed of 1.9 x 107 m/s is just barely captured by a nucleus with a diameter of 1.3 x 10-14 m. Assuming the strong force on the neutron is constant, find the magnitude of that force. (The neutron’s mass is 1.67×10-27 kg.)

F = ? N

[Hint: When the acceleration is constant, the velocity changes from vi to vf during the same interval. The average velocity over that interval is (vi + Vf)/2.]