A 2.30-g bullet embeds itself in a 1.10-kg block, which is attached to a spring of force constant 760N/m .

If the maximum compression of the spring is 5.60cm , find the initial speed of the bullet.

Question

A 2.30-g bullet embeds itself in a 1.10-kg block, which is attached to a spring of force constant 760N/m .

If the maximum compression of the spring is 5.60cm , find the initial speed of the bullet.

anonymous · Answer

for the mass, do I use just the mass of the bullet alone or do I also add in the mass of the block?

anonymous · Answer

Yep, add them together. It is the total mass that is acting on the spring.

anonymous · Answer

Ok. So I did what you guys told me and got the equation:

$$v =\sqrt{\frac{(760N/m)(0.056m)^2}{1.1023kg}}$$

Which gave me v=1.47m/s. The answer is wrong. What did I do wrong?

anas.p · Answer

I believe the mass should only be for the bullet as K.E. is only for bullet and not the block.
v=32.19 m/s

anonymous · Answer

Nope. I ran out of tries and the right answer is actually 705 m/s. Any idea how they got that answer?

schrodingers_cat · Answer

Well the problem is that this is a inelastic collision so

$$m _{b}v _{b} = (m _{b} +m _{bl})v _{bl}$$ 

Solving for the velocity of the block and using energy conservation you get

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