How to find the total momentum before and after a collision?

Physics... MOMENTUM plzzzz help 10 points.?

• 2. To find the velocity of a bullet, the bullet is fired into a stationary block of known mass. Using the Law of Conversation of Momentum, the velocity of the bullet can be calculated. A bullet of mass .05kg is fired and strikes a stationary wooden block of mass 5.0kg. The bullet becomes embedded in the block; the block with the bullet in it moves forward at 10 m/s. a. What is the total momentum of this system after the bullet becomes embedded in the block? b. What must be the total momentum of the bullet-block system before the collision? Explain how you know this. c. What was the velocity of the bullet before it struck the block? (The velocity of the block before it was struck by the bullet was??)

• Answer:

  This is a perfectly inelastic collision. a) Let m be the mass of the bullet, M the mass of the wooden block and V the velocity of the bullet+block. Total momentum = (m + M)V = (.05 kg + 5.0 kg) x 10m/s = 50 kg x m/s (Account for significant figures) b) According to the Law of Conversation of Momentum, the total momentum of a closed system of objects (which has no interactions with external agents) is constant. Therefore the momentum after the collision will be equal to the sum of the momenta of the bullet and block, respectively. Therefore the total momentum of the bullet-block system before the collision is 50 kg x m/s. c) Let m be the mass of the bullet, M the mass of the wooden block, v the speed of the bullet, v' the velocity of the wooden block and V the velocity of the bullet+block. According to the Law of Conversation of Momentum mv + Mv' = (m + M)V (.05 kg)v + 0 = 50 kg x m/s v = 1000 m/s Therefore velocity of the bullet before it struck the block is 1000 m/s.