题目内容：

帮个忙.
一个15g的子弹横着被打到了一个mass 2.5kg的木块里,然后就卡在里那木块里.
刚开始那木块是垂直的,撞击使木块摇晃,使它MASS的中心上升了15CM.找出子弹快要撞击到木块前的速度.
A 15g bullet is fired horizontally into a block of wood with mass 2.5 kg and embedded in the block.Initially the block of wood hangs vertically and the impact causes the block to swing so that its center of mass rise 15cm.find the velocity of the bullet just before the impact.

优质解答

v1 = speed of bullet
v2 = speed of wood after being hit
v1 * 15g = v2 * 2515g
1/2 * v2^2 = g * 0.15
v1 = (2515 / 15) * sqrt(2 * 9.8 * 0.15) = 287.5 (m/s)