Solving for the Speed of an 8kg Bullet

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SUMMARY

The discussion focuses on a physics problem involving an 8 kg bullet that embeds itself into a stationary 9 kg block of wood, resulting in a combined velocity of 40 cm/s post-impact. The solution utilizes the principle of conservation of momentum, indicating that the collision is inelastic since the bullet and wood move together after the impact. The key equation applied is the conservation of momentum, which states that the total momentum before the collision equals the total momentum after the collision.

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Homework Statement



An 8 kg bullet is fired into a stationary 9 kg block of wood which is free to move. The bullet is stopped in the wood which has a velocity of 40 cm/s after the impact. What was the speed of the bullet?

Homework Equations





The Attempt at a Solution

 
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use the conservation of momentum
 
Well we know from the question that the bullet gets lodged into the wood upon impact. What kind of collision would that be? Elastic or Inelastic? What kind of properties, specifically with conservation of momentum/kinetic energy does that collision contain?

Let me know if you need more help.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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