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​ = 10 mmunloaded

A machine rests on spring mounts, which compress by 10 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 = 10 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
k = 150 kN/mc = 1940 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 1940 N·s/m. Find the damping ratio ζ.

m = 100 kgk = 150 kN/mc = 1940 N·s/m
ζ =
4.Medium
k = 25 kN/mc = 100 N·s/mm = 10 kg

A 10 kg mass is supported by a spring with a stiffness of 25 kN/m and a viscous damper with a damping coefficient of 100 N·s/m. Find the damping ratio ζ.

m = 10 kgk = 25 kN/mc = 100 N·s/m
ζ =
5.Hard
k1​ = 40k2​ = 30k3​ = 25m = 100 kg

A 100 kg mass hangs from spring k₃ = 25 kN/m. The top of k₃ is attached to a rigid bar that hangs from two springs side by side, k₁ = 40 kN/m and k₂ = 30 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 = 40 kN/mk2 = 30 kN/mk3 = 25 kN/m
fn = Hz
6.Hard
k1​ = 30k2​ = 15m = 40 kg

A 40 kg mass hangs from two springs connected end to end (in series): the upper spring has k₁ = 30 kN/m and the lower one k₂ = 15 kN/m. Find the equivalent stiffness keq of the spring system in kN/m.

m = 40 kgk1 = 30 kN/mk2 = 15 kN/m
keq = kN/m

Answer key

  1. 1. fn = 4.985 Hz
  2. 2. fn = 7.882 Hz
  3. 3. ζ = 0.2505
  4. 4. ζ = 0.1
  5. 5. fn = 2.16 Hz
  6. 6. keq = 10 kN/m

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