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twotaileddemon

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The question is "A 2 kg block initially hangs at rest at the end of two 1-meter strings of negligible mass. A .003 kg bullet, moving horizontally with a speed of 1000 meters per second, strikes the block and becomes embedded in it. After the collision, the bullet/block combination swings upward, but does not rotate.

a. Caclulate the speed of the bullet/block combination after the collision.

I got 1.5 m/s for this. I did M1Vo1 + M2Vo2 = M3Vf and solved for Vf.

b. Calculate the ratio of the initial kinetic energy of the buillet to the kinetic energy of the bullet/block combination immediately after the collision.

I got 668:1. I used the equation .5MVf^2 - .5MVo^2 = .5 (.003kg)(1000 m/s)^2 = 1500 and 1/2MVf^2 = .5 (2.003)(1.5)^2 = 2.247, and so 1500:2.247 = 668:1

c. Calculate the maximum vertical height above the intial rest position reached by the bullet/block combination.

I'm not really sure how to do this one... would I just do something like .5MVo^2 + .5(9.8)(1) to get it? (kinetic energy + potential energy)

d. Suppose the bullet went through the block instead of imbedding in it. How would this affect the maximum height? Explain.

I said that the height would decrease because there would not be as much velocity since the bullet is slowed down by the force of the block.

I'm not really sure on my answers. I made my best attempt, and I was wondering if anyone could help/guide me through the problem so that I understand it without giving me the answers (until I get the right answer). If not, it's okay, I understand you all must be very busy ^^. Thanks in advance for reading this.

a. Caclulate the speed of the bullet/block combination after the collision.

I got 1.5 m/s for this. I did M1Vo1 + M2Vo2 = M3Vf and solved for Vf.

b. Calculate the ratio of the initial kinetic energy of the buillet to the kinetic energy of the bullet/block combination immediately after the collision.

I got 668:1. I used the equation .5MVf^2 - .5MVo^2 = .5 (.003kg)(1000 m/s)^2 = 1500 and 1/2MVf^2 = .5 (2.003)(1.5)^2 = 2.247, and so 1500:2.247 = 668:1

c. Calculate the maximum vertical height above the intial rest position reached by the bullet/block combination.

I'm not really sure how to do this one... would I just do something like .5MVo^2 + .5(9.8)(1) to get it? (kinetic energy + potential energy)

d. Suppose the bullet went through the block instead of imbedding in it. How would this affect the maximum height? Explain.

I said that the height would decrease because there would not be as much velocity since the bullet is slowed down by the force of the block.

I'm not really sure on my answers. I made my best attempt, and I was wondering if anyone could help/guide me through the problem so that I understand it without giving me the answers (until I get the right answer). If not, it's okay, I understand you all must be very busy ^^. Thanks in advance for reading this.

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