Bullet hits mass attached to spring with pic

  • Thread starter hodgepodge
  • Start date
  • #1
47
0

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
 

Answers and Replies

  • #2
54
0
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.
 
  • #3
343
1
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.
 
  • #4
47
0
spring constant is 200 n/m sorry forgot to add it
 
  • #5
343
1
In the cases that it sticks energy is NOT conserved but momentum always is.

[tex] m_{1}v_{1}+m{2}v_{2}=m{1}v_{3}+m{2}v_{3} [/tex]

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

Then again use energy.
 
  • #6
47
0
thanks once again bright wang
 

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