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 = 50 kN/mm = 150 kgx

A 150 kg mass hangs from a spring with a stiffness of 50 kN/m. Ignore damping. Find the natural circular frequency ωn in rad/s.

m = 150 kgk = 50 kN/m
ωn = rad/s
3.Medium
k = 80 kN/mc = 400 N·s/mm = 200 kg

A 200 kg mass is supported by a spring with a stiffness of 80 kN/m and a viscous damper with a damping coefficient of 400 N·s/m. Find the damping ratio ζ.

m = 200 kgk = 80 kN/mc = 400 N·s/m
ζ =
4.Medium
tx12 mm1 cycle8.8 mm

In a free-vibration test of a damped mass–spring system, a displacement peak of 12 mm is followed one cycle later by a peak of 8.8 mm. Find the damping ratio ζ.

x0 = 12 mmx1 = 8.8 mmn = 1
ζ =
5.Hard
k1​ = 60k2​ = 10m = 5 kg

A 5 kg mass hangs from two springs connected end to end (in series): the upper spring has k₁ = 60 kN/m and the lower one k₂ = 10 kN/m. Ignore damping and the masses of the springs. Find the natural frequency fn of vertical vibration in Hz.

m = 5 kgk1 = 60 kN/mk2 = 10 kN/m
fn = Hz
6.Hard
k1​ = 80k2​ = 12k3​ = 10m = 40 kg

A 40 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 = 80 kN/m and k₂ = 12 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 = 80 kN/mk2 = 12 kN/mk3 = 10 kN/m
fn = Hz

Answer key

  1. 1. fn = 4.551 Hz
  2. 2. ωn = 18.26 rad/s
  3. 3. ζ = 0.05
  4. 4. ζ = 0.0493
  5. 5. fn = 6.59 Hz
  6. 6. fn = 2.39 Hz

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