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posted by  pikachu22 on 6/6/2007 4:00:43 AM  |  status: Live  

help!!

Course Textbook Chapter Problem
Calculus Based Physics Fundamentals of Physics Extended (7th) by Halliday, Resnick, Walker 9 46P
Question Details:
Does anyone know how to solve this problem?
 
a bullet of mass 10 g strikes a ballistic pendulum of mass 2.0 kg. the center of mass of the pendulum rises a vertical distance of 12 cm. Assuming that the bullet remains embedded in the pendulum, calculate the bullet 's initial speed.

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posted by HungryHungryHippo on 6/6/2007 4:50:15 AM  |  status: Live
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pikachu22's comment:
"thanks very much."
Response Details:
This problem is solved in three steps, using conservation of energy and momentum.  First, calculate the potential energy of the pendulum with the bullet after it rises:

PE = mgh = (mbullet + mpend)gh
PE = (0.01kg + 2.0kg)(9.8m/s2)(0.12m) = 2.36 J

Next, calculate the initial kinetic energy the instant the bullet is embedded in the pendulum:

KEi = PEf
1/2 (2.01kg)v2 = 2.36 J
v2 = 2.35 m2/s2
v = 1.53 m/s

Finally, the initial momentum of the bullet equals the momentum of the bullet embedded in the pendulum:

pi = pf
mbvi = (mb + mp)vf
(0.01kg)vi = (2.01kg)(1.53 m/s)
vi = 308 m/s
Hope I have helped.  Anyone feel free to correct any mistake I may have made.
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