k k k
SOLUTION MANUAL
k
,ProblemskandkSolutionskSectionk1.1k(1.1kthroughk1.19)
1.1 ThekspringkofkFigurek1.2kisksuccessivelykloadedkwithkmasskandkthekcorrespondingk(stat
ic)kdisplacementkiskrecordedkbelow.k Plotkthekdatakandkcalculatekthekspring'skstiffness.k
Notekthatkthekdatakcontainksomekerror.k Alsokcalculatekthekstandardkdeviation.
m(kg) 10 11 12 13 14 15 16
x(m) 1.14 1.25 1.37 1.48 1.59 1.71 1.82
Solution:
Free-bodykdiagram: Fromkthekfree-
bodykdiagramkandkstatickequilibrium:
kx
kxk =k mgk k (gk=k 9.81mk/ksk2)
k kk =k mgk/kx
ki
m k=k =k 86.164
n
mg
20
Theksamplekstandardkdeviationkinkcom
putedkstiffnesskis:
n
2
m 15 i
k k i=1
=k 0.164
=
10
0 1 2
x
Plotkofkmasskinkkgkversuskdisplacementkinkm
Computationkofkslopekfromkmg/x
m(kg) x(m) k(N/m)
10 1.14 86.05
11 1.25 86.33
12 1.37 85.93
13 1.48 86.17
14 1.59 86.38
15 1.71 86.05
16 1.82 86.24
@
@sseeisism
micicisisoolalatitoionn
,1.2 Derivektheksolutionkofk m˙x˙k+kkxk=k0k andkplotkthekresultkforkatkleastktwokperiodskforkthekcase
withknk=k2krad/s,kx0k=k1kmm,kandkv0 5 mm/s.
k=
Solution:
Given:
mxk+kkxk =k0 (1)
Assume:k x(t)k=kaertk.k Then xk =kare and xk=kark e k.k Substitutekintokequationk(1)kto
rt 2 rt
:kget:
mar2ertk +kkaertk =k0
mr2k +kkk =k0
k
rk =k i
m
Thusktherekarektwoksolutions:
k k
k
k k
x1k =kc1e ,k andk x2k =kc2e k
k
wherek(n k =k2k rad/s
= m
Theksumkofkx1kandkx2kiskalsokaksolutionksokthatkthektotalksolutionkis:
xk=k xk +kx =kck e2itk +kck e2it
1 2 1 2
Substitutekinitialkconditions:kx0k=k1kmm,kv0k= 5 mm/s
xk(0)k=kc1k+kc2k =kx0k =k1kkc2k =k1kkc1,k andk v ( 0 ) k=kxk(0)k=k2ic1k k2ic2k 5 mm/s
=kv0k =
k2c1k+k2c2k= 5ki.k Combiningkthektwokunderlinedkexpressionsk(2keqskink2kunkowns):
1k 1k 5
2c1 +k2kk2c = =k i, k andk c =k + i
5
5kikk 2 4
1 2
4
c1 2
Thereforektheksolutionkis:
k1 k 2it
5 2it k1 5
xk=k k ik e +k+
kk i k e
k 4
4
k2 k2
UsingkthekEulerkformulaktokevaluatekthekexponentialktermskyields:
k1 5 k1
xk=k k 5
2
k k
@
@sseeisism
micicisisoolalatitoionn
, ik (cosk2tk+kiksink2tk)k+k k k+ ik (cosk2tkkiksink2tk)
4 k2 4
3k
(kx(tk)k=kcosk2tk+ 5 sink2tk= sin(2tk+k0.7297)
2 2
@
@sseeisism
micicisisoolalatitoionn