Soal dan Pembahasan Gerak Harmonik Sederhana

Simple Harmonic Motion
1.      Two springs with constants respectively equal to 150 N/m arranged in parallel as shown in the following figure. What is the period of structure ( the mass of object m is 3 kg)?
A.    http://fisikastudycenter.com/images/periode-susunan-pegas-paralel-5.png0,2 π s
B.     0,4 π s
C.     2,0 π s
D.    3,0 π s
E.     4,0 π s

2.      An object is vibrating until form a harmonic motion with an equation  y = 0,04 sin 20π t. The deviation of y is in meters, t is time in second. What is the amplitude and frequency?
A.    0,04 m and 5 Hz
B.     0,04 m and 10 Hz
C.     0,4 m and 10 Hz
D.    0,5 m and 5 Hz
E.     4 m and 5 Hz

3.      A mass of block is 0,5 kg, connected to a  light spring with constant 200 N/m. Then the system is oscillating harmonic. If we know the maximum deviation is 3 cm, the maximum speed is. . .
A.    0,1 m/s
B.     0,6 m/s
C.     1 m/s
D.    1,5 m/s
E.     2 m/s

4.      http://fisikastudycenter.com/images/periode-susunan-pegas-seri-4.pngTwo identical spring with equal constants of 200 N/m are arranged in series as shown in the following figure. Object m is 2 kg suspended on the lower end of the string. The period of the string is. . .
A.    0,2 π √2 s
B.     0,2 π √3 s
C.     2,0 π √2 s
D.    2,0 π √3 s
E.     3,0 π √2 s


5.      The mass of an object with moves in a harmonic is 400 kg at a frequency of 25 Hz and amplitude of 5 cm. What is the maximum acceleration of harmonic motion?
A.    5000π2 cm/s2
B.     500π2 cm/s2
C.     10800π2 cm/s2
D.    18570 π2 cm/s2
E.     18750π2 cm/s2




KEY ANSWER :
1.      A. 0,2 π s
2.      B. 0,04 m and 10 Hz
3.      B. 0,6 m/s
4.      A. 0,2 π √2 s
5.      E. 18750π2 cm/s2



SOLUTION :
1.      Given              : k        = 150 N/m
              m       = 3 kg
            Ask                  : T. . .
Answer            : kt       = k1 + k2
                                    = 150 + 150 = 300 N/m
                           T       = 2π √m/kt
                                    =  2π √3/300
                                    = 2π/10 = 0,2 π s

2.      Given              : y = 0,04 sin 20π t
  Deviation y   = meters
  Time              = second
Ask                  : amplitude and frequency. . .
Answer            : amplitudo atau A
y = 0,04 sin 20π t
        ↓
     A = 0,04 meter

frekuensi atau f
y = 0,04 sin 20π t
                   ↓
               ω = 20π

2πf = 20π
f = 10 Hz

3.      Given              : m = 0,5 kg
k = 200 N/m
ymaks = A = 3 cm = 0,03 m
            Ask                  : Vmax. . .
Answer            : vmaks = ω A

               2π
vmaks= ____ x  A
                T

                2π
vmaks = ______  x (0,03) = 0,6 m/s
               0,1 π

4.      Given              : k = 200 N/m
 m = 2 kg
            Ask                  : T. . .
            Answer            : 1/kt    = 1/k1 +1/k2
                                                = 1/200 + 1/200
                                       Kt     = 100 N/m
                                       T       = 2π √m/kt
                                                = 2π √2/100
= (2π √2) : 10 = 0,2 π √2 s
5.      Given              : m       = 400 kg
 F         = 25 Hz
Amplitude = 5 cm
Ask                  : maximum acceleration. . .
Answer            : a maks           = ώ2 A
= (2 πf)2 (5)
= (2π . 25)2.7,5
= 4π2.625.7,5
= 18.750π2 cm/s2

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