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 = 1.1 m1.25 m3.5 kg8 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 thin solid disc of mass 8 kg and radius 0.15 m fixed to its lower end. The disc swings in its own plane and its centre is 1.25 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 3.5 kgL = 1.1 mmdisc = 8 kgr = 0.15 md = 1.25 m
IO = kg·m²
2.Easy
L = 2 mGOd = 0.4 mm = 4 kg

A uniform slender rod of mass 4 kg and length 2 m rotates about an axis O perpendicular to the rod, 0.4 m from its centre G. Find its mass moment of inertia IO about that axis.

m = 4 kgL = 2 md = 0.4 m
IO = kg·m²
3.Medium
ω = ?1.5 kgL = 1.8 mm = 1 kg

A uniform slender rod of mass 1 kg and length 1.8 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 = 1 kgL = 1.8 mmball = 1.5 kgg = 9.81 m/s²
ω = rad/s
4.Medium
n = 2500 rpmT = 1840 N·m

A motor delivers a torque of 1840 N·m at 2500 rpm. Find its power output P in kW.

T = 1840 N·mn = 2500 rpm
P = kW
5.Hard
θ = 20°vs = 7.5 m

A solid cylinder starts from rest and rolls without slipping down a slope inclined at 20° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 7.5 m along the slope.

θ = 20°s = 7.5 mI = ½·m·r²g = 9.81 m/s²
v = m/s
6.Hard
5.5 m/sω

A solid cylinder of mass 16.5 kg rolls without slipping at 5.5 m/s. Find its total kinetic energy Ek.

m = 16.5 kgv = 5.5 m/sI = ½·m·r²
Ek = J

Answer key

  1. 1. IO = 14 kg·m²
  2. 2. IO = 1.973 kg·m²
  3. 3. ω = 3.448 rad/s
  4. 4. P = 481.7 kW
  5. 5. v = 5.792 m/s
  6. 6. Ek = 374.3 J

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