Spring, calculating length

  • #1

Homework Statement


http://img26.imageshack.us/i/1113001.jpg/

#12


Homework Equations



u=(1/2)kx^2
F=mg

The Attempt at a Solution



mg=(1/2)kx^2
√(2mg/k) = x

however, this is not any of the choices.
the correct answer is B)mg/k
 

Answers and Replies

  • #2
Doc Al
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mg=(1/2)kx^2
:confused: You seem to be setting a force equal to an energy. Not good.

What's the frequency of a mass on a spring? Of a simple pendulum? Compare.
 
  • #3
okay i got the frequency of a mass of a spring is
f=√(g/L)/2π
and of a simple pendulum
w=√(k/m)

if i set them equal to each other i get
L = mg/(2πk) which is almost right, but the 2π is disregarded in the answer. does anyone know why?
 
  • #4
Doc Al
Mentor
45,246
1,594
ω is the angular frequency, not the frequency. To get f from ω, divide by 2pi.
 

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