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​ = 25 mmunloaded

A machine rests on spring mounts, which compress by 25 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 = 25 mmg = 9.81 m/s²
fn = Hz
2.Easy
kmδst​ = 8 mmunloaded

A machine rests on spring mounts, which compress by 8 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 = 8 mmg = 9.81 m/s²
fn = Hz
3.Medium
tx15 mm5 cycles0.6 mm

In a free-vibration test of a damped mass–spring system, a displacement peak of 15 mm is followed 5 cycles later by a peak of 0.6 mm. Find the damping ratio ζ.

x0 = 15 mmx5 = 0.6 mmn = 5
ζ =
4.Medium
k = 2 kN/mζ = 0.3m = 8 kg

An 8 kg mass on a spring with a stiffness of 2 kN/m has a viscous damper giving a damping ratio of 0.3. Find the damped natural frequency fd of its free vibration in Hz.

m = 8 kgk = 2 kN/mζ = 0.3
fd = Hz
5.Hard
k1​ = 15k2​ = 5k3​ = 50m = 100 kg

A 100 kg mass hangs from spring k₃ = 50 kN/m. The top of k₃ is attached to a rigid bar that hangs from two springs side by side, k₁ = 15 kN/m and k₂ = 5 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 = 100 kgk1 = 15 kN/mk2 = 5 kN/mk3 = 50 kN/m
fn = Hz
6.Hard
k1​ = 5k2​ = 5m = 50 kg

A 50 kg mass hangs from two springs side by side (in parallel), with stiffnesses k₁ = 5 kN/m and k₂ = 5 kN/m. The mass stays level. Find the equivalent stiffness keq of the spring system in kN/m.

m = 50 kgk1 = 5 kN/mk2 = 5 kN/m
keq = kN/m

Answer key

  1. 1. fn = 3.153 Hz
  2. 2. fn = 5.573 Hz
  3. 3. ζ = 0.1019
  4. 4. fd = 2.401 Hz
  5. 5. fn = 1.902 Hz
  6. 6. keq = 10 kN/m

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