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Physics Questions Over Ballistic Pendulum

1. What kind of collision does conserve momentum? What kind of collision does not conserve mechanical energy?
2. A bullet with a mass of 52 grams moving with a speed of 100 m/s slams into and wedges in a 1.8 kilogram block of wood initially at rest. The block is supported by a string as in the diagram to the right. Which one, conservation of energy or conservation of momentum, can be applied to this situation? Why?
*The diagram just shows a block hanging from the ceiling from a string.
3. How high does the block in problem #2 swing after being hit by the bullet?
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1 Answer

1. All collisions conserve momentum. Inellastic collsion doesn conserve mechanical energy.
2. Conservation of momentum is applied in this situation. Mechanical energy will not be concerved because some of it will be lost as heat and sound energy.
3. Intial momentum of bullet = .052x100 = 5.2Kgm/s
Initial momentum of block = 1.8 x 0 = 0
just after collision final momentum of bullet and block = (0.052+1.8)v
as per conservation of momentum
5.2 = (0.052+1.8)v
v = 2.8 m/s
After collsion apply principal of conservation of mechanical energy as there is no loss of energy during swinging motion
loss of kinetic energy = gain in potential energy
1/2 (0.052+1.8) x 2.82 = (0.052+1.8) x g x h
h = height gained by block = 2.82/(2x9.8) = 0.4m