A mass–spring–damper is described by y″ + 7.2y′ + 36y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
1.Easy
y″ + 7.2y′ + 36y = 0
ζ =
2.Easy
For the equation y″ + 7y′ + 12y = 0, find the root r of the characteristic equation that is closest to zero. It sets how slowly the solution dies out.
y″ + 7y′ + 12y = 0
r =
3.Medium
Solve y″ + 4y′ + 4y = 0 with y(0) = 1 and y′(0) = -2. Find y(2).
y″ + 4y′ + 4y = 0y(0) = 1y′(0) = -2
y(2) =
4.Medium
Solve y″ + 2y′ + y = 0 with y(0) = 5 and y′(0) = 4. Find y(1.5).
y″ + 2y′ + y = 0y(0) = 5y′(0) = 4
y(1.5) =
5.Hard
Solve y″ + 2y′ + 26y = 0 with y(0) = 5 and y′(0) = 0 (released from rest). Find y(1.5); angles in radians.
y″ + 2y′ + 26y = 0y(0) = 5y′(0) = 0
y(1.5) =
6.Hard
A tank holds 400 L of water in which 10 kg of salt is dissolved. Brine with 0.25 kg of salt per litre flows in at 10 L/min, and the well-mixed solution flows out at the same rate. How much salt m is in the tank after 75 min?
V = 400 Lm0 = 10 kgc = 0.25 kg/Lr = 10 L/min
m = kg
Answer key
- 1. ζ = 0.6
- 2. r = −3
- 3. y(2) = 0.01832
- 4. y(1.5) = 4.128
- 5. y(1.5) = 0.596
- 6. m = 86.2 kg
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