# Bullet hits mass attached to spring with pic

## Homework Statement

A 20 gram bullet strikes a 15 kg mass attached to a spring. The mass aslides and compresses the spring by 12 cm. Calculate the velocity of the bullet initially.

Bullet............................Mass..........Spring
...D.............................I--------I
..................................I...........I~~~~~~~~|
.........................._____I_______I___________|

## The Attempt at a Solution

i was thinking to use (1/2) x (K) x (x squared) = (1/2) x (m) x (v squared)
then i was told to solve for p (momentum) (??) after using the above formula

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Your attempt is good. From that equation, you can find v (the speed of the mass just before it compresses the spring).
But what happens to the bullet? Does it get embedded in the mass? That information is important.

Hi, is the spring constant given? Yes, its different if the bullet stick with the mass or bounces off, but in this problem it should stick.

spring constant is 200 n/m sorry forgot to add it

In the cases that it sticks energy is NOT conserved but momentum always is.

$$m_{1}v_{1}+m{2}v_{2}=m{1}v_{3}+m{2}v_{3}$$

they stick soo mass and the bullet has the same velocity.

Then again use energy.

thanks once again bright wang