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.

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
Or = 0.2 mL = 1 m1.2 m4.5 kg5.5 kg

A pendulum is made of a uniform slender rod (4.5 kg, 1 m long) pivoted at its top end O, with a thin solid disc of mass 5.5 kg and radius 0.2 m fixed to its lower end. The disc swings in its own plane and its centre is 1.2 m below O. Find the mass moment of inertia IO of the pendulum about O.

mrod = 4.5 kgL = 1 mmdisc = 5.5 kgr = 0.2 md = 1.2 m
IO = kg·m²
2.Easy
k = 0.5 m0 → 1000 rpm120 kg

A flywheel of mass 120 kg with a radius of gyration of 0.5 m is accelerated uniformly from rest to 1000 rpm. The driving torque is a constant 120 N·m and friction can be ignored. How long t does this take?

m = 120 kgk = 0.5 mn1 = 0 rpmn2 = 1000 rpmT = 120 N·m
t = s
3.Medium
15 kgaαM = 7.5 kgR = 0.4 m

A 15 kg block hangs from a light cord wrapped around a pulley, a uniform solid disc of mass 7.5 kg and radius 0.4 m that turns on a frictionless horizontal axle. The block is released from rest. Use g = 9.81 m/s². Find the tension T in the cord.

m = 15 kgM = 7.5 kgR = 0.4 mg = 9.81 m/s²
T = N
4.Medium
L = 2 mm = 1.5 kgα

A uniform slender rod of mass 1.5 kg and length 2 m is pinned at one end and held horizontal. It is released from rest. Use g = 9.81 m/s². Find the acceleration atip of the free end just after release.

m = 1.5 kgL = 2 mg = 9.81 m/s²
atip = m/s²
5.Hard
340 m/s30 g0.24 mL = 0.6 m7 kgφ

A uniform slender rod of mass 7 kg and length 0.6 m hangs at rest from a frictionless pivot at its top end. A 30 g bullet moving horizontally at 340 m/s hits the rod 0.24 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 = 7 kgL = 0.6 mm = 30 gv = 340 m/sd = 0.24 mg = 9.81 m/s²
φ = °
6.Hard
500 m/s30 g0.88 mL = 1.7 m9 kg

A uniform slender rod of mass 9 kg and length 1.7 m hangs at rest from a frictionless pivot at its top end. A 30 g bullet moving horizontally at 500 m/s hits the rod 0.88 m below the pivot and stays embedded. Find the angular velocity ω of the rod just after the impact.

M = 9 kgL = 1.7 mm = 30 gv = 500 m/sd = 0.88 m
ω = rad/s

Answer key

  1. 1. IO = 9.53 kg·m²
  2. 2. t = 26.18 s
  3. 3. T = 29.43 N
  4. 4. atip = 14.71 m/s²
  5. 5. φ = 34.13 °
  6. 6. ω = 1.518 rad/s

Full step-by-step solutions: practise this topic on examproblems.com.