Determine the velocity at which the bullet-block system hits the ground.

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The discussion focuses on calculating the velocity of a bullet-block system after a bullet strikes a block of wood. The bullet has a mass of 0.0020 kg and a velocity of 300 m/s, while the block weighs 3.0 kg and is positioned 2.0 m above the ground. The initial velocity of the combined system is calculated using momentum conservation, yielding 0.2 m/s. The participants discuss the need to determine the final velocity upon impact with the ground, incorporating both horizontal and vertical components. The use of the Pythagorean theorem and kinematic equations is debated, with a suggestion that the horizontal distance is unnecessary for the final calculation.
tawko
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1. A bullet of mass 0.0020 kg and traveling at 300 m/s strikes the center of a 3.0 kg block of wood which is sitting on a fence post. The block of wood is 2.0 m above the ground.
I got the velocity using the eq (m1v1 + m2v2)/Mtotal = 0.2 m/s [correct if incorrect please]

I then got the horizontal distance by finding time and using x = v*t

Determine the velocity at which the bullet-block system hits the ground. Be sure to include an angle.

2. a^2 + b^2 = c^2 Vfinal = at + Vinitial Xfinal = 1/2at (m1v1 + m2v2) / Mtotal
3. I figured this would involve a right triangle, so I tried solving for the length of the sides. I believe this is where I went wrong. The height of the triangle is 6.272 because i used Vfinal=at+Vinitial, 9.8(.64)+0. I then used the Pythagorean theorem but the answer seemed strange. Thanks.
 
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You did it right as far as I can tell, though you don't need the horizontal distance for anything (don't give yourself more work than necessary). By legs of the right triangle, you mean the horizontal velocity and the vertical velocity, right? If so, you're good. :)
 
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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