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 kg2.5 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 solid sphere of mass 2.5 kg and radius 0.25 m fixed to its lower end. The centre of the sphere is 1.05 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2.5 kgL = 0.8 mmsphere = 2.5 kgr = 0.25 md = 1.05 m
IO = kg·m²
2.Easy
L = 2.8 mGOd = 0.6 mm = 10 kg

A uniform slender rod of mass 10 kg and length 2.8 m rotates about an axis O perpendicular to the rod, 0.6 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 10 kgL = 2.8 md = 0.6 m
IO = kg·m²
3.Medium
ω = ?4 kgL = 2.3 mm = 10 kg

A uniform slender rod of mass 10 kg and length 2.3 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 4 kg is fixed to its free end. 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 = 10 kgL = 2.3 mmball = 4 kgg = 9.81 m/s²
ω = rad/s
4.Medium
0.5 kgaαM = 7.5 kgR = 0.5 m

A 0.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 7.5 kg and radius 0.5 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the tension T in the cord.

m = 0.5 kgM = 7.5 kgR = 0.5 mg = 9.81 m/s²
T = N
5.Hard
θ = 25°vs = 2 m

A thin hoop 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 2 m along the slope.

θ = 25°s = 2 mI = m·r²g = 9.81 m/s²
v = m/s
6.Hard
θ = 10°vs = 8.5 m

A solid cylinder starts from rest and rolls without slipping down a slope inclined at 10° to the horizontal. Use g = 9.81 m/s². Its radius is 0.25 m. Find its angular velocity ω after it has rolled 8.5 m along the slope.

θ = 10°s = 8.5 mI = ½·m·r²g = 9.81 m/s²r = 0.25 m
ω = rad/s

Answer key

  1. 1. IO = 3.352 kg·m²
  2. 2. IO = 10.13 kg·m²
  3. 3. ω = 3.236 rad/s
  4. 4. T = 4.328 N
  5. 5. v = 2.88 m/s
  6. 6. ω = 17.58 rad/s

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