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 = 0.15 mL = 1.4 m1.55 m0.5 kg5 kg

A pendulum is made of a uniform slender rod (0.5 kg, 1.4 m long) pivoted at its top end O, with a thin solid disc of mass 5 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 1.55 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 1.4 mmdisc = 5 kgr = 0.15 md = 1.55 m
IO = kg·m²
2.Easy
L = 0.5 mGOd = 0.15 mm = 10.5 kg

A uniform slender rod of mass 10.5 kg and length 0.5 m rotates about an axis O perpendicular to the rod, 0.15 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 10.5 kgL = 0.5 md = 0.15 m
IO = kg·m²
3.Medium
10.5 kgaαM = 18 kgR = 0.45 m

A 10.5 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 18 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 angular acceleration α of the pulley.

m = 10.5 kgM = 18 kgR = 0.45 mg = 9.81 m/s²
α = rad/s²
4.Medium
3 kgaαM = 2 kgR = 0.2 m

A 3 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 2 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 speed v of the block after it has fallen 0.5 m.

m = 3 kgM = 2 kgR = 0.2 mg = 9.81 m/s²h = 0.5 m
v = m/s
5.Hard
100 m/s10 g1.33 mL = 1.7 m8 kg

A uniform slender rod of mass 8 kg and length 1.7 m hangs at rest from a frictionless pivot at its top end. A 10 g bullet moving horizontally at 100 m/s hits the rod 1.33 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 8 kgL = 1.7 mm = 10 gv = 100 m/sd = 1.33 m
ω = rad/s
6.Hard
disc: 10 kgring: 6 kgn1​ = 150 rpm

A uniform solid disc (mass 10 kg, radius 0.45 m) spins freely at 150 rpm about a vertical frictionless shaft. A thin ring of mass 6 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. How much kinetic energy ΔE is lost in the process?

Mdisc = 10 kgMring = 6 kgR = 0.45 mn1 = 150 rpm
ΔE = J

Answer key

  1. 1. IO = 12.4 kg·m²
  2. 2. IO = 0.455 kg·m²
  3. 3. α = 11.74 rad/s²
  4. 4. v = 2.712 m/s
  5. 5. ω = 0.1722 rad/s
  6. 6. ΔE = 68.13 J

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