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 = 1.1 m1.35 m3.5 kg6.5 kg

A pendulum is made of a uniform slender rod (3.5 kg, 1.1 m long) pivoted at its top end O, with a solid sphere of mass 6.5 kg and radius 0.25 m fixed to its lower end. The centre of the sphere is 1.35 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 1.1 mmsphere = 6.5 kgr = 0.25 md = 1.35 m
IO = kg·m²
2.Easy
k = 0.25 m700 → 2600 rpm10 kg

A flywheel of mass 10 kg with a radius of gyration of 0.25 m is accelerated uniformly from 700 rpm to 2600 rpm. The driving torque is a constant 9.6 N·m and friction can be ignored. How long t does this take?

m = 10 kgk = 0.25 mn1 = 700 rpmn2 = 2600 rpmT = 9.6 N·m
t = s
3.Medium
n = 2500 rpmTb​ = 65 N·mI = 14.5 kg·m²

A flywheel with a moment of inertia of 14.5 kg·m² spins at 2500 rpm. A brake applies a constant friction torque of 65 N·m. How long t does it take to stop?

I = 14.5 kg·m²n = 2500 rpmTb = 65 N·m
t = s
4.Medium
7.5 kgaαM = 6.5 kgR = 0.35 m

A 7.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 6.5 kg and radius 0.35 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 = 7.5 kgM = 6.5 kgR = 0.35 mg = 9.81 m/s²
T = N
5.Hard
380 m/s15 g0.73 mL = 1.2 m5 kgφ

A uniform slender rod of mass 5 kg and length 1.2 m hangs at rest from a frictionless pivot at its top end. A 15 g bullet moving horizontally at 380 m/s hits the rod 0.73 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 = 5 kgL = 1.2 mm = 15 gv = 380 m/sd = 0.73 mg = 9.81 m/s²
φ = °
6.Hard
7.5 m/sω

A solid cylinder of mass 3 kg rolls without slipping at 7.5 m/s. What percentage p of its total kinetic energy is rotational?

m = 3 kgv = 7.5 m/sI = ½·m·r²
p = %

Answer key

  1. 1. IO = 13.42 kg·m²
  2. 2. t = 12.95 s
  3. 3. t = 58.4 s
  4. 4. T = 22.24 N
  5. 5. φ = 28.56 °
  6. 6. p = 33.33 %

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