DC motors worksheet with answers

Free printable DC motors worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

New worksheetPractise online with hints

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
+−110 VRa​Ia​ = 40 AM+−EωT = ?

A permanent-magnet DC motor has the torque constant k = 1.5 N·m/A. Find the torque T it develops at an armature current of 40 A.

k = 1.5 N·m/AIa = 40 A
T = N·m
2.Easy
+−48 VRa​ = 0.4 ΩIa​ = 4 AM+−En = ?T

A DC motor with k = 0.75 V·s/rad and an armature resistance of 0.4 Ω runs from 48 V and draws 4 A. Find its speed n in rpm.

V = 48 VRa = 0.4 ΩIa = 4 Ak = 0.75 V·s/rad
n = rpm
3.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 15 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 15 kWn = 1200 rpm
T = N·m
4.Medium
T (N·m)n (rpm)3.6 N·mn0​n = ?

A DC motor (k = 0.3 N·m/A, Ra = 0.2 Ω) runs from 48 V and drives a load torque of 3.6 N·m. Find its speed n in rpm.

V = 48 Vk = 0.3 N·m/ARa = 0.2 ΩT = 3.6 N·m
n = rpm
5.Hard
T (N·m)n (rpm)40 N·m1500 rpm

A DC motor with k = 1 V·s/rad and Ra = 0.25 Ω must drive a load of 40 N·m at 1500 rpm. Find the armature voltage V it needs.

k = 1 V·s/radRa = 0.25 ΩT = 40 N·mn = 1500 rpm
V = V
6.Hard
+−24 VRs​ = ?Ra​ = 0.4 ΩM+−En = 600 rpmT = 1.2 N·m

A DC motor (k = 0.3 V·s/rad, Ra = 0.4 Ω) on a fixed 24 V supply drives a load of 1.2 N·m. Find the series resistance Rs that slows it down to 600 rpm.

V = 24 Vk = 0.3 V·s/radRa = 0.4 ΩT = 1.2 N·mn = 600 rpm
Rs = Ω

Answer key

  1. 1. T = 60 N·m
  2. 2. n = 590.8 rpm
  3. 3. T = 119.4 N·m
  4. 4. n = 1451 rpm
  5. 5. V = 167.1 V
  6. 6. Rs = 0.8876 Ω

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