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 = 1.5 m1.75 m4.5 kg1.5 kg

A pendulum is made of a uniform slender rod (4.5 kg, 1.5 m long) pivoted at its top end O, with a solid sphere of mass 1.5 kg and radius 0.25 m fixed to its lower end. The centre of the sphere is 1.75 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 4.5 kgL = 1.5 mmsphere = 1.5 kgr = 0.25 md = 1.75 m
IO = kg·m²
2.Easy
Or = 0.05 mL = 1.2 m1.25 m1.5 kg3.5 kg

A pendulum is made of a uniform slender rod (1.5 kg, 1.2 m long) pivoted at its top end O, with a thin solid disc of mass 3.5 kg and radius 0.05 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 = 1.5 kgL = 1.2 mmdisc = 3.5 kgr = 0.05 md = 1.25 m
IO = kg·m²
3.Medium
n = 1700 rpmP = 141.5 kW

A shaft transmits 141.5 kW at 1700 rpm. Find the torque T in the shaft.

P = 141.5 kWn = 1700 rpm
T = N·m
4.Medium
ω = ?2 kgL = 1.4 mm = 6.5 kg

A uniform slender rod of mass 6.5 kg and length 1.4 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 2 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 = 6.5 kgL = 1.4 mmball = 2 kgg = 9.81 m/s²
ω = rad/s
5.Hard
380 m/s40 g0.58 mL = 0.7 m6.5 kg

A uniform slender rod of mass 6.5 kg and length 0.7 m hangs at rest from a frictionless pivot at its top end. A 40 g bullet moving horizontally at 380 m/s hits the rod 0.58 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 6.5 kgL = 0.7 mm = 40 gv = 380 m/sd = 0.58 m
ω = rad/s
6.Hard
θ = 30°vs = 7.5 m

A solid sphere starts from rest and rolls without slipping down a slope inclined at 30° to the horizontal. Use g = 9.81 m/s². Find its speed v after it has rolled 7.5 m along the slope.

θ = 30°s = 7.5 mI = (2/5)·m·r²g = 9.81 m/s²
v = m/s

Answer key

  1. 1. IO = 8.006 kg·m²
  2. 2. IO = 6.193 kg·m²
  3. 3. T = 794.8 N·m
  4. 4. ω = 4.202 rad/s
  5. 5. ω = 8.2 rad/s
  6. 6. v = 7.249 m/s

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