- #1
Dennis Heerlein
- 19
- 0
Homework Statement
A ballistic pendulum is a device that may be used to measure the muzzle speed of a bullet. It is composed of a wooden block suspended from a horizontal support by cords attached at each end. A bullet is shot into the block, and as a result of the perfectly inelastic impact, the block swings upward. Consider a bullet (mass m) with velocity v as it enters the block (mass M). The length of the cords supporting the block each have length L. The maximum height to which the block swings upward after impact is denoted by y, and the maximum horizontal displacement is denoted by x.
a) In terms of m, M, g and y, determine the speed of the bullet.
Homework Equations
mgh=1/2 m v2
The Attempt at a Solution
(1/2)(m)v2 = (m + M)(g)(y)
v =sqroot { [(2)(g)(m + M)(y)]/m }
The real solution states that one must find the initial velocity of the bullet-block system, and then use this equation. Why can I not just use the initial velocity of the bullet? The real final answer is what I have, except the (m+M)/m is outside the sqroot.