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 = 0.2 mL = 1.4 m1.6 m4.5 kg4.5 kg

A pendulum is made of a uniform slender rod (4.5 kg, 1.4 m long) pivoted at its top end O, with a solid sphere of mass 4.5 kg and radius 0.2 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 = 4.5 kgL = 1.4 mmsphere = 4.5 kgr = 0.2 md = 1.6 m
IO = kg·m²
2.Easy
R = 0.25 mn = 2300 rpm20 kg

A flywheel is a uniform solid disc of mass 20 kg and radius 0.25 m. It spins at 2300 rpm. Find its kinetic energy Ek in kJ.

M = 20 kgR = 0.25 mn = 2300 rpm
Ek = kJ
3.Medium
ω = ?L = 0.9 mm = 3.5 kg

A uniform slender rod of mass 3.5 kg and length 0.9 m is pinned at one end and released from rest in a horizontal position. 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 = 3.5 kgL = 0.9 mg = 9.81 m/s²
ω = rad/s
4.Medium
v = ?2.5 kgL = 0.8 mm = 3.5 kg

A uniform slender rod of mass 3.5 kg and length 0.8 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 2.5 kg is fixed to its free end. Ignore friction and use g = 9.81 m/s². Find the speed v of the free end as the rod swings through the vertical position.

m = 3.5 kgL = 0.8 mmball = 2.5 kgg = 9.81 m/s²
v = m/s
5.Hard
θ = 10°a

A solid cylinder rolls without slipping down a slope inclined at 10° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 10°I = ½·m·r²g = 9.81 m/s²
a = m/s²
6.Hard
θ = 15°as = 8 m

A solid cylinder rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². It starts from rest. How long t does it take to roll 8 m down the slope?

θ = 15°I = ½·m·r²g = 9.81 m/s²s = 8 m
t = s

Answer key

  1. 1. IO = 14.53 kg·m²
  2. 2. Ek = 18.13 kJ
  3. 3. ω = 5.718 rad/s
  4. 4. v = 4.265 m/s
  5. 5. a = 1.136 m/s²
  6. 6. t = 3.074 s

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