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 = 1.2 m1.4 m1.5 kg4 kg

A pendulum is made of a uniform slender rod (1.5 kg, 1.2 m long) pivoted at its top end O, with a solid sphere of mass 4 kg and radius 0.2 m fixed to its lower end. The centre of the sphere is 1.4 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 1.2 mmsphere = 4 kgr = 0.2 md = 1.4 m
IO = kg·m²
2.Easy
Or = 0.2 mL = 0.7 m0.9 m3.5 kg4.5 kg

A pendulum is made of a uniform slender rod (3.5 kg, 0.7 m long) pivoted at its top end O, with a thin solid disc of mass 4.5 kg and radius 0.2 m fixed to its lower end. The disc swings in its own plane and its centre is 0.9 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 0.7 mmdisc = 4.5 kgr = 0.2 md = 0.9 m
IO = kg·m²
3.Medium
5 kgaαM = 6.5 kgR = 0.2 m

A 5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 6.5 kg and radius 0.2 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the acceleration a of the block.

m = 5 kgM = 6.5 kgR = 0.2 mg = 9.81 m/s²
a = m/s²
4.Medium
ω = ?L = 1.5 mm = 9 kg

A uniform slender rod of mass 9 kg and length 1.5 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 = 9 kgL = 1.5 mg = 9.81 m/s²
ω = rad/s
5.Hard
θ = 35°as = 2.5 m

A hollow sphere rolls without slipping down a slope inclined at 35° to the horizontal. Use g = 9.81 m/s². It starts from rest. How long t does it take to roll 2.5 m down the slope?

θ = 35°I = (2/3)·m·r²g = 9.81 m/s²s = 2.5 m
t = s
6.Hard
θ = 40°vs = 9.5 m

A hollow sphere starts from rest and rolls without slipping down a slope inclined at 40° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 9.5 m along the slope.

θ = 40°s = 9.5 mI = (2/3)·m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 8.624 kg·m²
  2. 2. IO = 4.307 kg·m²
  3. 3. a = 5.945 m/s²
  4. 4. ω = 4.429 rad/s
  5. 5. t = 1.217 s
  6. 6. v = 8.479 m/s

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