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 = 0.7 m0.8 m3 kg1 kg

A pendulum is made of a uniform slender rod (3 kg, 0.7 m long) pivoted at its top end O, with a solid sphere of mass 1 kg and radius 0.1 m fixed to its lower end. The centre of the sphere is 0.8 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3 kgL = 0.7 mmsphere = 1 kgr = 0.1 md = 0.8 m
IO = kg·m²
2.Easy
k = 0.5 m700 → 1100 rpm140 kg

A flywheel of mass 140 kg with a radius of gyration of 0.5 m is accelerated uniformly from 700 rpm to 1100 rpm. The driving torque is a constant 51 N·m and friction can be ignored. How long t does this take?

m = 140 kgk = 0.5 mn1 = 700 rpmn2 = 1100 rpmT = 51 N·m
t = s
3.Medium
n = 2200 rpmTb​ = 25 N·mI = 37 kg·m²

A flywheel with a moment of inertia of 37 kg·m² spins at 2200 rpm. A brake applies a constant friction torque of 25 N·m. How long t does it take to stop?

I = 37 kg·m²n = 2200 rpmTb = 25 N·m
t = s
4.Medium
L = 1.3 mm = 9 kgα

A uniform slender rod of mass 9 kg and length 1.3 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 = 9 kgL = 1.3 mg = 9.81 m/s²
R = N
5.Hard
1 m/sω

A hollow sphere of mass 6 kg rolls without slipping at 1 m/s. Find its total kinetic energy Ek.

m = 6 kgv = 1 m/sI = (2/3)·m·r²
Ek = J
6.Hard
θ = 40°a

A solid sphere rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find the smallest coefficient of static friction μs that prevents it from slipping.

θ = 40°I = (2/5)·m·r²g = 9.81 m/s²
μs =

Answer key

  1. 1. IO = 1.134 kg·m²
  2. 2. t = 28.75 s
  3. 3. t = 341 s
  4. 4. R = 22.07 N
  5. 5. Ek = 5 J
  6. 6. μs = 0.2397

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