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​ = 12 mmunloaded

A machine rests on spring mounts, which compress by 12 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 = 12 mmg = 9.81 m/s²
fn = Hz
2.Easy
k = 5 kN/mm = 2 kgx

A 2 kg mass hangs from a spring with a stiffness of 5 kN/m. Ignore damping. Find the natural frequency fn in Hz.

m = 2 kgk = 5 kN/m
fn = Hz
3.Medium
tx50 mm1 cycle41.4 mm

In a free-vibration test of a damped mass–spring system, a displacement peak of 50 mm is followed one cycle later by a peak of 41.4 mm. Find the damping ratio ζ.

x0 = 50 mmx1 = 41.4 mmn = 1
ζ =
4.Medium
k = 150 kN/mc = 4650 N·s/mm = 100 kg

A 100 kg mass is supported by a spring with a stiffness of 150 kN/m and a viscous damper with a damping coefficient of 4650 N·s/m. Find the damping ratio ζ.

m = 100 kgk = 150 kN/mc = 4650 N·s/m
ζ =
5.Hard
k1​ = 80k2​ = 25k3​ = 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 = 80 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 = 100 kgk1 = 80 kN/mk2 = 25 kN/mk3 = 50 kN/m
fn = Hz
6.Hard
k1​ = 100k2​ = 50m = 40 kg

A 40 kg mass hangs from two springs side by side (in parallel), with stiffnesses k₁ = 100 kN/m and k₂ = 50 kN/m. The mass stays level. Find the equivalent stiffness keq of the spring system in kN/m.

m = 40 kgk1 = 100 kN/mk2 = 50 kN/m
keq = kN/m

Answer key

  1. 1. fn = 4.551 Hz
  2. 2. fn = 7.958 Hz
  3. 3. ζ = 0.03003
  4. 4. ζ = 0.6003
  5. 5. fn = 2.929 Hz
  6. 6. keq = 150 kN/m

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