Mechanical vibrations worksheet with answers

Free printable Mechanical vibrations worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
kmδst​ = 1 mmunloaded

A machine rests on spring mounts, which compress by 1 mm under its weight. Treat it as an undamped single-degree-of-freedom system and use g = 9.81 m/s². Find the natural frequency fn of vertical vibration in Hz.

δst = 1 mmg = 9.81 m/s²
fn = Hz
2.Easy
k = 40 kN/mm = 12 kgx

A 12 kg mass hangs from a spring with a stiffness of 40 kN/m. Ignore damping. Find the natural circular frequency ωn in rad/s.

m = 12 kgk = 40 kN/m
ωn = rad/s
3.Medium
tx15 mm4 cycles7.1 mm

In a free-vibration test of a damped mass–spring system, a displacement peak of 15 mm is followed 4 cycles later by a peak of 7.1 mm. Find the damping ratio ζ.

x0 = 15 mmx4 = 7.1 mmn = 4
ζ =
4.Medium
k = 12 kN/mc = 280 N·s/mm = 40 kg

A 40 kg mass is supported by a spring with a stiffness of 12 kN/m and a viscous damper with a damping coefficient of 280 N·s/m. Find the damping ratio ζ.

m = 40 kgk = 12 kN/mc = 280 N·s/m
ζ =
5.Hard
k1​ = 80k2​ = 15m = 10 kg

A 10 kg mass hangs from two springs side by side (in parallel), with stiffnesses k₁ = 80 kN/m and k₂ = 15 kN/m. The mass stays level. Ignore damping and the masses of the springs. Find the natural frequency fn of vertical vibration in Hz.

m = 10 kgk1 = 80 kN/mk2 = 15 kN/m
fn = Hz
6.Hard
k1​ = 25k2​ = 25k3​ = 40m = 40 kg

A 40 kg mass hangs from spring k₃ = 40 kN/m. The top of k₃ is attached to a rigid bar that hangs from two springs side by side, k₁ = 25 kN/m and k₂ = 25 kN/m; the bar stays level. Ignore damping and the masses of the springs and bar. Find the natural frequency fn of vertical vibration in Hz.

m = 40 kgk1 = 25 kN/mk2 = 25 kN/mk3 = 40 kN/m
fn = Hz

Answer key

  1. 1. fn = 15.76 Hz
  2. 2. ωn = 57.74 rad/s
  3. 3. ζ = 0.02975
  4. 4. ζ = 0.2021
  5. 5. fn = 15.51 Hz
  6. 6. fn = 3.751 Hz

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