A bullet of mass $125$ gms strikes a fixed block of wood horizontally with a velocity of $100$ metres/seconds. The resistance of the wood is $500$ kg-weight. Show that the distance through which the bullet goes into the wood before being brought to rest $12.5$ cm.
Attempt: I understand that block of wood is fixed and will not move after the impact. That means how to apply the principle of conservation of linear momentum? Please help me to solve the problem.
If I assume that $d$ is the distance penetrated, then "work done = change of energy" principle implies $Resistance~ \times d= \frac{1}{2}\frac{125}{1000}(100)^2$
i.e $d=25/20=1.25$ meter=$125$ cm.
Please check my result (answer is $12.5$ cm).
Yes the resistance is $500g$ not $500$
Comservation of linear momentum only applies to objects which are free to move, so it does not apply here. The Work Energy Principle is the correct approach.