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​ = 2 mmunloaded

A machine rests on spring mounts, which compress by 2 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 = 2 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
k = 2 kN/mc = 20 N·s/mm = 20 kg

A 20 kg mass is supported by a spring with a stiffness of 2 kN/m and a viscous damper with a damping coefficient of 20 N·s/m. Find the damping ratio ζ.

m = 20 kgk = 2 kN/mc = 20 N·s/m
ζ =
4.Medium
tx20 mm1 cycle15.6 mm

In a free-vibration test of a damped mass–spring system, a displacement peak of 20 mm is followed one cycle later by a peak of 15.6 mm. Find the damping ratio ζ.

x0 = 20 mmx1 = 15.6 mmn = 1
ζ =
5.Hard
k1​ = 15k2​ = 25k3​ = 12m = 25 kg

A 25 kg mass hangs from spring k₃ = 12 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 = 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 = 25 kgk1 = 15 kN/mk2 = 25 kN/mk3 = 12 kN/m
fn = Hz
6.Hard
k1​ = 25k2​ = 25m = 5 kg

A 5 kg mass hangs from two springs side by side (in parallel), with stiffnesses k₁ = 25 kN/m and k₂ = 25 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 = 5 kgk1 = 25 kN/mk2 = 25 kN/m
fn = Hz

Answer key

  1. 1. fn = 11.15 Hz
  2. 2. fn = 5.573 Hz
  3. 3. ζ = 0.05
  4. 4. ζ = 0.03951
  5. 5. fn = 3.058 Hz
  6. 6. fn = 15.92 Hz

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