A bullet of mass is fired into a stationary block of mass at some velocity . The block is attached to a wire (assume massless and infinitely rigid). The bullet-block system swings to a height .
Part 1: Explain why the conservation of energy cannot be applied before the collision?
Part 2: Determine in terms of , , and .
Part 3: Suppose the block is 100 times heavier than the bullet. If the bullet-block system swings to a height of 20 cm, what was the velocity of the bullet? Assume this setup is on Earth.
Energy is only conserved in perfectly elastic collisions. Since this collision is inelastic, energy is not conserved prior to collision and during the collision. However, kinetic energy of the bullet-block system is conserved post collision, which is converted to gravitational potential energy.
Conservation of momentum (before and during collision).
Conservation of energy (post collision).
From the conservation of momentum