- #1

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## Homework Statement

A 7-g bullet is fired into a 1.5-kg ballistic pendulum. The bullet emerges from the block with a speed of 200 m/s, and the block rises to a maximum height of 12 cm. Find the initial speed of the bullet.

## Homework Equations

conservation of momentum

## The Attempt at a Solution

First I tried to find the initial momentum of the bullet as if it did't penetrate the block

so .007v

_{i}= (1.507)v

_{f}

because I have two unknowns I used the conservation of mechanical energy to solve for v

_{f}

1/2(1.507)(v

_{f}

^{2}) = (1.507)(9.8)(.12)

v

_{f}= 1.54 m/s

then plug that in to find the initial velocity

v

_{i}= 435.29 m/s

initial momentum = 3.05

Then I tried to find the momentum of the bullet exiting the block and add it to the initial momentum to get the total initial momentum.

200(.007) = 1.4

1.4 + 3.05 = 4.45

and finally I divided that by the mass to get the initial velocity 635.75 m/s. The correct answer is 529 m/s.