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 = 0.5 m0.6 m2 kg5 kg

A pendulum is made of a uniform slender rod (2 kg, 0.5 m long) pivoted at its top end O, with a solid sphere of mass 5 kg and radius 0.1 m fixed to its lower end. The centre of the sphere is 0.6 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 2 kgL = 0.5 mmsphere = 5 kgr = 0.1 md = 0.6 m
IO = kg·m²
2.Easy
k = 0.45 m300 → 1200 rpm10 kg

A flywheel of mass 10 kg with a radius of gyration of 0.45 m is accelerated uniformly from 300 rpm to 1200 rpm. The driving torque is a constant 7.1 N·m and friction can be ignored. How long t does this take?

m = 10 kgk = 0.45 mn1 = 300 rpmn2 = 1200 rpmT = 7.1 N·m
t = s
3.Medium
v = ?L = 2.1 mm = 10 kg

A uniform slender rod of mass 10 kg and length 2.1 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 speed v of the free end as the rod swings through the vertical position.

m = 10 kgL = 2.1 mg = 9.81 m/s²
v = m/s
4.Medium
n = 1800 rpmP = 39.5 kW

A shaft transmits 39.5 kW at 1800 rpm. Find the torque T in the shaft.

P = 39.5 kWn = 1800 rpm
T = N·m
5.Hard
460 m/s15 g0.43 mL = 0.7 m8 kg

A uniform slender rod of mass 8 kg and length 0.7 m hangs at rest from a frictionless pivot at its top end. A 15 g bullet moving horizontally at 460 m/s hits the rod 0.43 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 8 kgL = 0.7 mm = 15 gv = 460 m/sd = 0.43 m
ω = rad/s
6.Hard
520 m/s10 g0.78 mL = 1.2 m6 kgφ

A uniform slender rod of mass 6 kg and length 1.2 m hangs at rest from a frictionless pivot at its top end. A 10 g bullet moving horizontally at 520 m/s hits the rod 0.78 m below the pivot and stays embedded. Use g = 9.81 m/s². Find the largest angle φ from the vertical through which the rod swings.

M = 6 kgL = 1.2 mm = 10 gv = 520 m/sd = 0.78 mg = 9.81 m/s²
φ = °

Answer key

  1. 1. IO = 1.987 kg·m²
  2. 2. t = 26.88 s
  3. 3. v = 7.861 m/s
  4. 4. T = 209.6 N·m
  5. 5. ω = 2.266 rad/s
  6. 6. φ = 23.15 °

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