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2 questions about momentum

發問:

1. A gun fired vertically into a 1.40kg block of wood at rest directly above it. If the bullet has a mass of 21.0g and a speed of 210m/s, how high will the block rise into the air after the bullet becomes embedded in it?** according to the back of my book, the answer is 0.4912 . After a... 顯示更多 1. A gun fired vertically into a 1.40kg block of wood at rest directly above it. If the bullet has a mass of 21.0g and a speed of 210m/s, how high will the block rise into the air after the bullet becomes embedded in it? ** according to the back of my book, the answer is 0.491 2 . After a completely inelastic collision between two objects of equal mass, each having initial speed (v), the two move off together with speed v/3. What was the angle between their initial directions?

最佳解答:

1. By the law of conservation of momentum mu = (m + M)v (0.021)(210) = (0.021 + 1.40)v Speed of the block just after the impact, v = 3.103 ms-1 Then, by the law of conservation of energy Loss of K.E. = Gain of G.P.E. 1/2 mv2 = mgh 1/2 (3.103)2 = (9.8)h Height gained, h = 0.491 m 圖片參考：http://i182.photobucket.com/albums/x4/A_Hepburn_1990/A_Hepburn01Feb121505.jpg?t=1234422435 圖片參考：http://i182.photobucket.com/albums/x4/A_Hepburn_1990/A_Hepburn03Feb121506.jpg?t=1234422448

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