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.

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
Or = 0.25 mL = 1.4 m1.65 m0.5 kg7 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.4 m long) pivoted at its top end O, with a thin solid disc of mass 7 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 1.65 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.4 mmdisc = 7 kgr = 0.25 md = 1.65 m
IO = kg·m²
2.Easy
Or = 0.2 mL = 1.1 m1.3 m3 kg1 kg

A pendulum is made of a uniform slender rod (3 kg, 1.1 m long) pivoted at its top end O, with a solid sphere of mass 1 kg and radius 0.2 m fixed to its lower end. The centre of the sphere is 1.3 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3 kgL = 1.1 mmsphere = 1 kgr = 0.2 md = 1.3 m
IO = kg·m²
3.Medium
n = 2200 rpmTb​ = 55 N·mI = 16.5 kg·m²

A flywheel with a moment of inertia of 16.5 kg·m² spins at 2200 rpm. A brake applies a constant friction torque of 55 N·m. How many revolutions N does the flywheel make before it stops?

I = 16.5 kg·m²n = 2200 rpmTb = 55 N·m
N = rev
4.Medium
L = 0.9 mm = 3.5 kgα

A uniform slender rod of mass 3.5 kg and length 0.9 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find the vertical force R that the pin exerts on the rod just after release.

m = 3.5 kgL = 0.9 mg = 9.81 m/s²
R = N
5.Hard
disc: 30 kgring: 13 kgn1​ = 250 rpm

A uniform solid disc (mass 30 kg, radius 0.3 m) spins freely at 250 rpm about a vertical frictionless shaft. A thin ring of mass 13 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. Find their common speed n2 in rpm.

Mdisc = 30 kgMring = 13 kgR = 0.3 mn1 = 250 rpm
n2 = rpm
6.Hard
disc: 10 kgring: 6 kgn1​ = 450 rpm

A uniform solid disc (mass 10 kg, radius 0.2 m) spins freely at 450 rpm about a vertical frictionless shaft. A thin ring of mass 6 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. Find their common speed n2 in rpm.

Mdisc = 10 kgMring = 6 kgR = 0.2 mn1 = 450 rpm
n2 = rpm

Answer key

  1. 1. IO = 19.6 kg·m²
  2. 2. IO = 2.916 kg·m²
  3. 3. N = 1267 rev
  4. 4. R = 8.584 N
  5. 5. n2 = 133.9 rpm
  6. 6. n2 = 204.5 rpm

Full step-by-step solutions: practise this topic on examproblems.com.