How Do You Calculate the Mass of a Block from a Bullet and Spring Collision?

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SUMMARY

The discussion focuses on calculating the mass of a wooden block after a bullet embeds itself in it and compresses a spring. A 34g bullet traveling at 120m/s collides with the block, which compresses a spring with a spring constant of 99N/m by 1.2 cm. The conservation of momentum and energy equations are applied: m1v1 + m2v2 = (m1 + m2)v' and Ee = 0.5kx². The analysis confirms that the mass of the block must be significantly large due to the minimal compression of the spring.

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Homework Statement


A 34g bullet traveling at 120m/s embeds itself in a wooden block on a smooth surface. The block then slides toward a spring and collides with it. The block compresses the spring (k=99N/m) a maximum of 1.2 cm. Calculate the mass of the block of wood.


Homework Equations


Not sure.
m1v1 + m2v2 = (m1 + m2)v'
Ee = .5kx2
Ek = .5mv2


The Attempt at a Solution


I'm fairly certain it's incorrect. I just don't know where.
IMG_NEW.jpg


Thanks!
 
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I see your concern with the mass of the wooden block. Your approach is correct. Consider the spring. It has a spring constant of 99N/m. This means if the spring were used as a scale a 10 kg mass would compress the spring 1 meter. A very weak spring. Since the spring compressed .012 meters your answer is reasonable; the velocity of the bullet-block system would have to be very small meaning a very large mass for the block.
 

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