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 = 0.2 mL = 0.6 m0.8 m2.5 kg1.5 kg

A pendulum is made of a uniform slender rod (2.5 kg, 0.6 m long) pivoted at its top end O, with a thin solid disc of mass 1.5 kg and radius 0.2 m fixed to its lower end. The disc swings in its own plane and its centre is 0.8 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2.5 kgL = 0.6 mmdisc = 1.5 kgr = 0.2 md = 0.8 m
IO = kg·m²
2.Easy
R = 0.25 mn = 2000 rpm300 kg

A flywheel is a uniform solid disc of mass 300 kg and radius 0.25 m. It spins at 2000 rpm. Find its kinetic energy Ek in kJ.

M = 300 kgR = 0.25 mn = 2000 rpm
Ek = kJ
3.Medium
n = 3000 rpmT = 1510 N·m

A motor delivers a torque of 1510 N·m at 3000 rpm. Find its power output P in kW.

T = 1510 N·mn = 3000 rpm
P = kW
4.Medium
ω = ?2.5 kgL = 2.3 mm = 9 kg

A uniform slender rod of mass 9 kg and length 2.3 m is pinned at one end and released from rest in a horizontal position. A small ball of mass 2.5 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 = 9 kgL = 2.3 mmball = 2.5 kgg = 9.81 m/s²
ω = rad/s
5.Hard
580 m/s35 g0.35 mL = 0.5 m1.5 kg

A uniform slender rod of mass 1.5 kg and length 0.5 m hangs at rest from a frictionless pivot at its top end. A 35 g bullet moving horizontally at 580 m/s hits the rod 0.35 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 1.5 kgL = 0.5 mm = 35 gv = 580 m/sd = 0.35 m
ω = rad/s
6.Hard
400 m/s50 g1.5 mL = 1.5 m5.5 kg

A uniform slender rod of mass 5.5 kg and length 1.5 m hangs at rest from a frictionless pivot at its top end. A 50 g bullet moving horizontally at 400 m/s hits the rod 1.5 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 5.5 kgL = 1.5 mm = 50 gv = 400 m/sd = 1.5 m
ω = rad/s

Answer key

  1. 1. IO = 1.29 kg·m²
  2. 2. Ek = 205.6 kJ
  3. 3. P = 474.4 kW
  4. 4. ω = 3.295 rad/s
  5. 5. ω = 54.96 rad/s
  6. 6. ω = 7.08 rad/s

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