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​ = 0.5 mmunloaded

A machine rests on spring mounts, which compress by 0.5 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 = 0.5 mmg = 9.81 m/s²
fn = Hz
2.Easy
kmδst​ = 4 mmunloaded

A machine rests on spring mounts, which compress by 4 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 = 4 mmg = 9.81 m/s²
fn = Hz
3.Medium
tx12 mm5 cycles6.4 mm

In a free-vibration test of a damped mass–spring system, a displacement peak of 12 mm is followed 5 cycles later by a peak of 6.4 mm. Find the damping ratio ζ.

x0 = 12 mmx5 = 6.4 mmn = 5
ζ =
4.Medium
k = 200 kN/mζ = 0.4m = 100 kg

A 100 kg mass on a spring with a stiffness of 200 kN/m has a viscous damper giving a damping ratio of 0.4. Find the damped natural frequency fd of its free vibration in Hz.

m = 100 kgk = 200 kN/mζ = 0.4
fd = Hz
5.Hard
k1​ = 60k2​ = 60k3​ = 10m = 10 kg

A 10 kg mass hangs from spring k₃ = 10 kN/m. The top of k₃ is attached to a rigid bar that hangs from two springs side by side, k₁ = 60 kN/m and k₂ = 60 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 = 10 kgk1 = 60 kN/mk2 = 60 kN/mk3 = 10 kN/m
fn = Hz
6.Hard
k1​ = 100k2​ = 5m = 20 kg

A 20 kg mass hangs from two springs side by side (in parallel), with stiffnesses k₁ = 100 kN/m and k₂ = 5 kN/m. The mass stays level. Find the equivalent stiffness keq of the spring system in kN/m.

m = 20 kgk1 = 100 kN/mk2 = 5 kN/m
keq = kN/m

Answer key

  1. 1. fn = 22.29 Hz
  2. 2. fn = 7.882 Hz
  3. 3. ζ = 0.02001
  4. 4. fd = 6.523 Hz
  5. 5. fn = 4.835 Hz
  6. 6. keq = 105 kN/m

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