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 = 0.25 mL = 0.8 m1.05 m2.5 kg6.5 kg

A pendulum is made of a uniform slender rod (2.5 kg, 0.8 m long) pivoted at its top end O, with a thin solid disc of mass 6.5 kg and radius 0.25 m fixed to its lower end. The disc swings in its own plane and its centre is 1.05 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2.5 kgL = 0.8 mmdisc = 6.5 kgr = 0.25 md = 1.05 m
IO = kg·m²
2.Easy
L = 2.1 mGOd = 0.75 mm = 6 kg

A uniform slender rod of mass 6 kg and length 2.1 m rotates about an axis O perpendicular to the rod, 0.75 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 6 kgL = 2.1 md = 0.75 m
IO = kg·m²
3.Medium
L = 2.8 mm = 9.5 kgα

A uniform slender rod of mass 9.5 kg and length 2.8 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 = 9.5 kgL = 2.8 mg = 9.81 m/s²
R = N
4.Medium
L = 2.2 mm = 14.5 kgα

A uniform slender rod of mass 14.5 kg and length 2.2 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 = 14.5 kgL = 2.2 mg = 9.81 m/s²
atip = m/s²
5.Hard
θ = 15°vs = 5 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 5 m along the slope.

θ = 15°s = 5 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s
6.Hard
θ = 30°vs = 5.5 m

A hollow sphere starts from rest and rolls without slipping down a slope inclined at 30° to the horizontal. Use g = 9.81 m/s². Its radius is 0.2 m. Find its angular velocity ω after it has rolled 5.5 m along the slope.

θ = 30°s = 5.5 mI = (2/3)·m·r²g = 9.81 m/s²r = 0.2 m
ω = rad/s

Answer key

  1. 1. IO = 7.903 kg·m²
  2. 2. IO = 5.58 kg·m²
  3. 3. R = 23.3 N
  4. 4. atip = 14.71 m/s²
  5. 5. v = 4.259 m/s
  6. 6. ω = 28.45 rad/s

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