Elastic PE and K Notes

PE and k

e) PE_s in terms of k

1. P.E._s = Fx

Average Force: F = F/2

2. PE = (F/2)x

substitute F = Kx (On reference)

3. P.E._s = (1/2)(Kx)x

P.E._s = 1/2(kx²)

(On reference)

Ex 1) A force of 12. N stretches a spring and makes it .15m longer

a) What the spring constant (k) of this spring?

Ex 1) A force of 12. N stretches a spring and makes it .15m longer

a) What's the spring constant (k) of this spring?

k = F/x

= 12. N/.15 m

= 80. N/m

b) P.E. of this spring?

PE_s = (½)Kx²

= 1/2(80. N/m)(.15 m)²

PE_s = .90 Joules

Ex 2) If 15. joules of energy are stored in the stretched spring below, what is the value of the spring constant

Ex 2) If 15. joules of energy are stored in the stretched spring, what is the value of the spring constant

P.E._s = 1/2(kx²)

15. J = (½)K(.50 m)²

15. J = .50 k(.25)

= 120 N/m

P.E._s = 1/2(kx²)

What's wrong with this picture?

P.E._s = 1/2(kx²)

PE, X direct square

Plot should be curved