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 = 0.1 mL = 0.4 m0.5 m4.5 kg8 kg

A pendulum is made of a uniform slender rod (4.5 kg, 0.4 m long) pivoted at its top end O, with a solid sphere of mass 8 kg and radius 0.1 m fixed to its lower end. The centre of the sphere is 0.5 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 4.5 kgL = 0.4 mmsphere = 8 kgr = 0.1 md = 0.5 m
IO = kg·m²
2.Easy
Or = 0.1 mL = 1.3 m1.4 m1 kg9.5 kg

A pendulum is made of a uniform slender rod (1 kg, 1.3 m long) pivoted at its top end O, with a solid sphere of mass 9.5 kg and radius 0.1 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 kgL = 1.3 mmsphere = 9.5 kgr = 0.1 md = 1.4 m
IO = kg·m²
3.Medium
n = 2900 rpmT = 730 N·m

A motor delivers a torque of 730 N·m at 2900 rpm. Find its power output P in kW.

T = 730 N·mn = 2900 rpm
P = kW
4.Medium
ω = ?1.5 kgL = 0.5 mm = 4 kg

A uniform slender rod of mass 4 kg and length 0.5 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 1.5 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 = 4 kgL = 0.5 mmball = 1.5 kgg = 9.81 m/s²
ω = rad/s
5.Hard
disc: 28 kgring: 11 kgn1​ = 100 rpm

A uniform solid disc (mass 28 kg, radius 0.4 m) spins freely at 100 rpm about a vertical frictionless shaft. A thin ring of mass 11 kg and the same radius is dropped onto it from rest, centred on the shaft, and the two quickly spin together. Find their common speed n2 in rpm.

Mdisc = 28 kgMring = 11 kgR = 0.4 mn1 = 100 rpm
n2 = rpm
6.Hard
θ = 15°vs = 6 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 15° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 6 m along the slope.

θ = 15°s = 6 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 2.272 kg·m²
  2. 2. IO = 19.22 kg·m²
  3. 3. P = 221.7 kW
  4. 4. ω = 6.962 rad/s
  5. 5. n2 = 56 rpm
  6. 6. v = 4.665 m/s

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