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 = 0.7 m0.9 m2 kg7.5 kg

A pendulum is made of a uniform slender rod (2 kg, 0.7 m long) pivoted at its top end O, with a thin solid disc of mass 7.5 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 = 2 kgL = 0.7 mmdisc = 7.5 kgr = 0.2 md = 0.9 m
IO = kg·m²
2.Easy
Or = 0.2 mL = 0.9 m1.1 m1.5 kg4 kg

A pendulum is made of a uniform slender rod (1.5 kg, 0.9 m long) pivoted at its top end O, with a thin solid disc of mass 4 kg and radius 0.2 m fixed to its lower end. The disc swings in its own plane and its centre is 1.1 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 1.5 kgL = 0.9 mmdisc = 4 kgr = 0.2 md = 1.1 m
IO = kg·m²
3.Medium
3 kgaαM = 3 kgR = 0.45 m

A 3 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 3 kg and radius 0.45 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the speed v of the block after it has fallen 3.5 m.

m = 3 kgM = 3 kgR = 0.45 mg = 9.81 m/s²h = 3.5 m
v = m/s
4.Medium
n = 3000 rpmTb​ = 40 N·mI = 5 kg·m²

A flywheel with a moment of inertia of 5 kg·m² spins at 3000 rpm. A brake applies a constant friction torque of 40 N·m. How many revolutions N does the flywheel make before it stops?

I = 5 kg·m²n = 3000 rpmTb = 40 N·m
N = rev
5.Hard
θ = 20°a

A solid sphere rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². Find the acceleration a of its centre.

θ = 20°I = (2/5)·m·r²g = 9.81 m/s²
a = m/s²
6.Hard
280 m/s30 g0.72 mL = 1.3 m9.5 kgφ

A uniform slender rod of mass 9.5 kg and length 1.3 m hangs at rest from a frictionless pivot at its top end. A 30 g bullet moving horizontally at 280 m/s hits the rod 0.72 m below the pivot and stays embedded. Use g = 9.81 m/s². Find the largest angle φ from the vertical through which the rod swings.

M = 9.5 kgL = 1.3 mm = 30 gv = 280 m/sd = 0.72 mg = 9.81 m/s²
φ = °

Answer key

  1. 1. IO = 6.552 kg·m²
  2. 2. IO = 5.325 kg·m²
  3. 3. v = 6.766 m/s
  4. 4. N = 981.7 rev
  5. 5. a = 2.397 m/s²
  6. 6. φ = 19.28 °

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