- #1

Abu

- 39

- 16

- Homework Statement
- A spring of negligible mass has force constant k = 800 N/m. You place the spring vertically with one end on the floor. You then lay a 1.6 kg block on top of the spring and release the book from rest. Find the maximum distance the spring will be compressed

- Relevant Equations
- F = kx

Hi everyone, just a quick question..

I tried this problem using Newtons laws, not conservation of energy, and I got an answer exactly half of what the correct answer is, and I'm not sure why. Here is what I did:

Net force = zero once the spring is compressed, therefore

mg - kx = 0

mg = kx

mg/k = x

1.6(9.8)/800 = x

x = 1.96 cm

The actual answer is 3.92 cm however, and I don't know why.

If I do this problem using conservation of energy, I get the correct answer but I can't explain why my Newtons laws method is wrong.

Thanks for your consideration!

I tried this problem using Newtons laws, not conservation of energy, and I got an answer exactly half of what the correct answer is, and I'm not sure why. Here is what I did:

Net force = zero once the spring is compressed, therefore

mg - kx = 0

mg = kx

mg/k = x

1.6(9.8)/800 = x

x = 1.96 cm

The actual answer is 3.92 cm however, and I don't know why.

If I do this problem using conservation of energy, I get the correct answer but I can't explain why my Newtons laws method is wrong.

Thanks for your consideration!