Forensic scientists can measure the muzzle velocity of a gun by firing a bullet

Question

Forensic scientists can measure the muzzle velocity of a gun by firing a bullet horizontally into a large hanging block that absorbs the bullet and swings upward. The measured maximum angle of swing can be used to calculate the speed of the bullet. In one such test, a rifle fired a 4.20 g bullet into a 2.50 kg block hanging by a thin wire 75.0 cm long, causing the block to swing upward to a maximum angle of 34.7ofrom the vertical.

a.Use energy conservation and the picture from part a to determine how fast the block and bullet are moving after the collision.

b.What was the original speed of this bullet?

Explanation / Answer

a) mgh(1-cos34.7 = 1/2mv^2

v = sqrt[2gh(1-cos34.70] = 1.62 m/s

b)m1u = (m1+m2)v

u = 959.9 m/s

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