Bullet hits mass attached to spring with pic

[hodgepodge]

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___________|

Homework Equations

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

 

[visharad]

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.

 

[glueball8]

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.

 

[hodgepodge]

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

 

[glueball8]

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.

 

[hodgepodge]

thanks once again bright wang