# Energy not conserved?

Let us suppose a stone of $$4$$kg mass falls from $$5$$ meter above upon an iron rod of the same mass which was entering the ground. Consequently the rod entered $$10$$ cm more deep into the ground.

Now considering the head of the iron rod as reference level total energy initially is that of the stone which is $$m_{1}gh_{1}=4\times10\times 5=200$$. Now after the rod has hit the ground $$0.1$$ meter deep, both the stone and rod's velocity becomes $$0$$ and so final energy of the system is $$m_{2}g(-h_{2})=4\times 10 \times (-0.1)$$. As we can see the energy has not been conserved. Where did i go wrong in this problem?

• I think the stone's velocity might non-zero at that point,it then gives $\frac{1}{2}m_{1}v^2-m_{2}gh_{2}$ on the right hand side. Oct 21, 2021 at 11:12