**Solution:**

Mass of Hammer, m = 1 kg

Initial Velocity, u = 6 m/s

Final Velocity, v = 0 m/s

Time Taken, t = 0.1 s

The acceleration is: a = (v – u )/t

a = ( 0 m/s – 6 m/s ) / 0.1 sec

Therefore, a = – 60 m/s^{2}

[-ve sign means retardation]

Thus, the retarding Force, F = ma = 1 × 60 = 60 N