# Bullet Hitting Wood the Spring, check of solution

 P: 610 Bullet Hitting Wood the Spring, check of solution ok now you got the velocity of the bullet+block system. Now find the expression for the kinetic energy of this system , with velocity, $$v=\frac{10}{m_b +m_w}$$ Now use the conservation of energy. some of this energy will be turned into internal energy due to friction and some of it will be converted into the elastic potential energy of the spring. and 0.05 times 200 is not 100, its 10. careful about arithmetic in physics class
 P: 610 the block and bullet together slide. the kinetic energy lost during the inelastic collision is already gone ( in the form of sound etc)Now we have the kinetic energy of the system at our disposal. Think of energy as the nature's currency. Now we have to spend this remaining currency. Part of it will be spent in work related to the friction and other part will be stored in the spring. While using energy approach to do physics problems, always think of 'energy transfer'. I don't like to use the language of "work done" etc. Energy is an universal thing in the world. Always think of 'energy transfer' while doing such problems. Always ask, where did my energy go (like bankers always check the money in their account) ? And one more piece of advice while doing physics problems. ALWAYS use vector notation wherever possible. Then your calculations will never be wrong. Intro physics textbooks have the habit of converting a vector equation into a scalar equation involving the magnitudes. But if you stick with the vector notation, then the signs arising out of the vectors will be taken care of automatically since you specify vectors with the directions. This is very important in Work-energy related problems because , the $\pm$ signs have deep meaning. + means energy is added into the system and - means energy is taken out of the system (and converted to some other form). Now where I am located, in India, its late night. So your further questions, I will answer tomorrow.