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Please help me =D

  • #1
A 35.0-g bullet strikes a 4.7-kg stationary piece of lumber and embeds itself in the wood. The piece of lumber and bullet fly off together at 8.0 m/s. What was the original speed of the bullet?
I don't know where to begin...
 

Answers and Replies

  • #2
This one too pleeasee

A thread holds a 1.5-kg and a 4.50-kg cart together. After the thread is burned, a compressed spring pushes the carts apart, giving the 1.5 kg cart a speed of 27 cm/s to the left. What is the velocity of the 4.5-kg cart?



I would be so grateful if someone could help me..
 
  • #3
rl.bhat
Homework Helper
4,433
5
Just go through the conservation of linear momentum.
 
  • #4
3,003
2
Hi there. Is conservation of linear momentum something you have studied in class? :smile:

Also: I would start a new thread for each problem, else things get confusing/messy.
 
  • #5
Yes, im in the ib program but i was absent for that lesson..
ha thanks for the heads up, i just started this
Andd thank you both for the help
 
  • #6
3,003
2
Yes, im in the ib program but i was absent for that lesson..
ha thanks for the heads up, i just started this
Andd thank you both for the help

Okay, well paraphrasing Conservation of momentum says that if no external forces act on a system (which is true in this case), then the total linear momentum is conserved.

That is, [itex]\sum mv_{initial}=\sum mv_{final}[/itex]

In this case,

[tex]M_{bullet}V_{bullet}+M_{block}V_{block}=M_{(block+bullet)}V'_{(block+bullet)}[/tex]

where I used the ' symbol to indicate velocity after the collision

And Yes, they are both conservation of momentum.
 
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