Calculating Spring Constant with Hanging Spring and Mass

[dmolson]

I have a problem I cannot figure out. It asks to calculate the spring constant when given a spring hung from the ceiling, a 0.497 kg block attached to the free end of the spring. The block is released from rest, drops 0.12 m before coming momentarily to rest. How do I calculate the spring constant?? Please Help!

 

[radou]

What does the force in a spring equal?

 

[dmolson]

F = -kx I thought

 

[radou]

Right. That's one of the forces acting on the block. Which is the other one? What is the relation between these two forces in order for the block to be in equilibrium?

 

[dmolson]

Right. That's one of the forces acting on the block. Which is the other one? What is the relation between these two forces in order for the block to be in equilibrium?

The other one would be gravity (mg) acting on the block. I thought the relation was F = kx - mg. But I do not know for sure.

 

[radou]

The other one would be gravity (mg) acting on the block. I thought the relation was F = kx - mg. But I do not know for sure.

If there was a non-zero net force F, as you stated, the block wouldn't be at rest. The problem states that the block came to rest, after the spring extended for some amount x. So, if the block is at rest, the net force must equal zero. Hence, kx = mg.

 

[dmolson]

I tried that solution and it did not work. Here is the original problem.

A spring is hung from the ceiling. A 0.497-kg block is then attached to the free end of the spring. When released from rest, the block drops 0.12 m before momentarily coming to rest. What is the spring constant?

 

[radou]

Interesting, it should work, unless I'm missing something enormous here. Do you know the solution?

 

[dmolson]

No, it is part of the e-homework I have. The next part says to calculate the angular frequency. I only have limited tries and I have tried the second part.

 

[dmolson]

*have not tried