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 = 0.05 mL = 0.8 m0.85 m4 kg1.5 kg

A pendulum is made of a uniform slender rod (4 kg, 0.8 m long) pivoted at its top end O, with a solid sphere of mass 1.5 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.85 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 4 kgL = 0.8 mmsphere = 1.5 kgr = 0.05 md = 0.85 m
IO = kg·m²
2.Easy
k = 0.4 m400 → 1200 rpm190 kg

A flywheel of mass 190 kg with a radius of gyration of 0.4 m is accelerated uniformly from 400 rpm to 1200 rpm. The driving torque is a constant 180 N·m and friction can be ignored. How long t does this take?

m = 190 kgk = 0.4 mn1 = 400 rpmn2 = 1200 rpmT = 180 N·m
t = s
3.Medium
L = 1.9 mm = 6 kgα

A uniform slender rod of mass 6 kg and length 1.9 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 = 6 kgL = 1.9 mg = 9.81 m/s²
atip = m/s²
4.Medium
L = 1 mm = 10 kgα

A uniform slender rod of mass 10 kg and length 1 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find its angular acceleration α just after release.

m = 10 kgL = 1 mg = 9.81 m/s²
α = rad/s²
5.Hard
θ = 40°a

A solid cylinder rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 40°I = ½·m·r²g = 9.81 m/s²
a = m/s²
6.Hard
θ = 25°vs = 6 m

A solid cylinder starts from rest and rolls without slipping down a slope inclined at 25° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 6 m along the slope.

θ = 25°s = 6 mI = ½·m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 1.939 kg·m²
  2. 2. t = 14.15 s
  3. 3. atip = 14.71 m/s²
  4. 4. α = 14.71 rad/s²
  5. 5. a = 4.204 m/s²
  6. 6. v = 5.759 m/s

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