Elastic Potential Energy and Hooke's Law.notebook
May 16, 2014
Elastic Potential Energy
When you stretch or compress a spring or other elastic object,
you do work against the spring force
That work is stored as elastic potential energy
The force is F = kx
x is the sitance the spring is stretched from equilibrium (resting state)
k is the force constant of teh spring in newtons per metre N/m
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Elastic Potential Energy and Hooke's Law.notebook
May 16, 2014
Example
A spring whose force constatn is 48 N/m has a 2.4 N weight suspended from it
What is the extension of the spring
F = kx
x = F/k
x = 2.4N/ 48 N/m
x = .050m (5.0 cm)
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Elastic Potential Energy and Hooke's Law.notebook
May 16, 2014
Ex:
1.
What force is necessary to stetch a spring whose force constant is 120N/m by an amount of 30cm?
F = kx 120N/m x 0.30m = 36 N
2.
A spring in a pogo stick is compressed 12 cm when a 390N boy stands on the stick
What is the force constant for the pogo stick's spring?
k = F/x = 390N/ 0.12m = 3250N/m
3.
A spring with a force constant of 600 N/m is used in a scale for weighing fish
What is the weight of the fish that stretches the spring 7.5 cm from its normal length?
F = kx = 600N/m x 0.075m = 45N
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Elastic Potential Energy and Hooke's Law.notebook
May 16, 2014
Force (N)
y
100
96
92
88
84
80
76
72
68
64
60
56
52
48
44
40
36
32
28
24
20
16
12
8
4
0
2
4
6
8
10
12
14
k will be the slope
k = F/x (in metres)
Work will be the area
under the curve
(F x x )/2
x
16
18
20
Displacement (cm)
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Elastic Potential Energy and Hooke's Law.notebook
May 16, 2014
Energy stored in a spring
The Elastic potential energy Epe
K spring constant (N/m)
elongation (compression)
of the spring (m)
Ex: the length of a spring is increased
by 10.0 cm when a force of 20.0 N is
applied to it. Calculate the elaxtic
potential energy stored in this spirng
First caclulate the spring constant
Fr = F = kx
20.0N = k 0.100m
k= 200N/m
Epe = 1/2 (200N/m) 0.100m = 10.0J
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