Rigid-body rotation worksheet with answers

Free printable Rigid-body rotation 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
Or = 0.1 mL = 1.5 m1.6 m3 kg2.5 kg

A pendulum is made of a uniform slender rod (3 kg, 1.5 m long) pivoted at its top end O, with a solid sphere of mass 2.5 kg and radius 0.1 m fixed to its lower end. The centre of the sphere is 1.6 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3 kgL = 1.5 mmsphere = 2.5 kgr = 0.1 md = 1.6 m
IO = kg·m²
2.Easy
R = 0.2 mn = 1800 rpm70 kg

A flywheel is a uniform solid disc of mass 70 kg and radius 0.2 m. It spins at 1800 rpm. Find its kinetic energy Ek in kJ.

M = 70 kgR = 0.2 mn = 1800 rpm
Ek = kJ
3.Medium
L = 1.8 mm = 9.5 kgα

A uniform slender rod of mass 9.5 kg and length 1.8 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find the acceleration atip of the free end just after release.

m = 9.5 kgL = 1.8 mg = 9.81 m/s²
atip = m/s²
4.Medium
ω = ?3.5 kgL = 2 mm = 6 kg

A uniform slender rod of mass 6 kg and length 2 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 3.5 kg is fixed to its free end. Ignore friction and use g = 9.81 m/s². Find the angular velocity ω of the rod as it swings through the vertical position.

m = 6 kgL = 2 mmball = 3.5 kgg = 9.81 m/s²
ω = rad/s
5.Hard
3 m/sω

A hollow sphere of mass 6 kg rolls without slipping at 3 m/s. Find its rotational kinetic energy Erot.

m = 6 kgv = 3 m/sI = (2/3)·m·r²
Erot = J
6.Hard
disc: 32 kgring: 8 kgn1​ = 850 rpm

A uniform solid disc (mass 32 kg, radius 0.45 m) spins freely at 850 rpm about a vertical frictionless shaft. A thin ring of mass 8 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. How much kinetic energy ΔE is lost in the process?

Mdisc = 32 kgMring = 8 kgR = 0.45 mn1 = 850 rpm
ΔE = J

Answer key

  1. 1. IO = 8.66 kg·m²
  2. 2. Ek = 24.87 kJ
  3. 3. atip = 14.71 m/s²
  4. 4. ω = 3.405 rad/s
  5. 5. Erot = 18 J
  6. 6. ΔE = 4278 J

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