A ballistic pendulum is used to measure the speed of bullets. It comprises a heavy block of wood of mass M suspended by two long cords. A bullet of mass m is fired into the block in the horizontal direction. The block, with the bullet embedded in it, swings upward (see figure below). The center of mass of the combination rises through a vertical distance h before coming to rest momentarily. In a particular experiment, a bullet of mass 48.0 g is fired into a wooden block of mass 11.2 kg. The block–bullet combination is observed to rise to a maximum height of 19.6 cm above the block's initial height.

(a) What is the initial speed of the bullet?


(b) What is the fraction of initial kinetic energy lost after the bullet is embedded in the block? (Enter your answer to at least three significant figures.)

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  1. (a) momentum is conserved ... .0480 Vib = (11.2 + .048) Vbb
    ... (Vbb)^2 = 2 * g * 0.0196

    (b) KEb = 1/2 * 0.0480 * (Vib)^2 ... this is KEm
    ... KEbb = 11.248 * g * 0.0196 ... this is KEM+m

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