A hammer of mass M strikes a nail of mass m with velocity of u m/s and drives it a metre into fixed block of wood. The average resistance of wood to the penetration of nail is

Applying the conservation of momentummu=(M+m)v0∴v0=MM+muThe acceleration A can be obtained using the formulav2=u2+2asHere A is negative, y =0, u = v0 and s = a∴02=v02−2Aa  or  A=v02/2a or A=Mm+M2u22aResistance =(M+m)A=M2(M+m)×u22a.