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 = 0.05 mL = 0.9 m0.95 m0.5 kg8.5 kg

A pendulum is made of a uniform slender rod (0.5 kg, 0.9 m long) pivoted at its top end O, with a solid sphere of mass 8.5 kg and radius 0.05 m fixed to its lower end. The centre of the sphere is 0.95 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 0.5 kgL = 0.9 mmsphere = 8.5 kgr = 0.05 md = 0.95 m
IO = kg·m²
2.Easy
k = 0.1 m0 → 1900 rpm50 kg

A flywheel of mass 50 kg with a radius of gyration of 0.1 m is accelerated uniformly from rest to 1900 rpm. This takes 21 s. Ignoring friction, find the constant torque T needed.

m = 50 kgk = 0.1 mn1 = 0 rpmn2 = 1900 rpmt = 21 s
T = N·m
3.Medium
n = 1500 rpmT = 1130 N·m

A motor delivers a torque of 1130 N·m at 1500 rpm. Find its power output P in kW.

T = 1130 N·mn = 1500 rpm
P = kW
4.Medium
ω = ?L = 2.4 mm = 7.5 kg

A uniform slender rod of mass 7.5 kg and length 2.4 m is pinned at one end and released from rest in a horizontal position. 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 = 7.5 kgL = 2.4 mg = 9.81 m/s²
ω = rad/s
5.Hard
360 m/s10 g0.67 mL = 0.8 m3 kg

A uniform slender rod of mass 3 kg and length 0.8 m hangs at rest from a frictionless pivot at its top end. A 10 g bullet moving horizontally at 360 m/s hits the rod 0.67 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 3 kgL = 0.8 mm = 10 gv = 360 m/sd = 0.67 m
ω = rad/s
6.Hard
560 m/s10 g0.25 mL = 0.5 m6.5 kg

A uniform slender rod of mass 6.5 kg and length 0.5 m hangs at rest from a frictionless pivot at its top end. A 10 g bullet moving horizontally at 560 m/s hits the rod 0.25 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 6.5 kgL = 0.5 mm = 10 gv = 560 m/sd = 0.25 m
ω = rad/s

Answer key

  1. 1. IO = 7.815 kg·m²
  2. 2. T = 4.737 N·m
  3. 3. P = 177.5 kW
  4. 4. ω = 3.502 rad/s
  5. 5. ω = 3.742 rad/s
  6. 6. ω = 2.582 rad/s

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