A mass–spring–damper is described by y″ + 1.5y′ + 9y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
1.Easy
y″ + 1.5y′ + 9y = 0
ζ =
2.Easy
A bacterial culture starts with 5000 cells and grows according to dN/dt = k·N with k = 0.3 h⁻¹. After how many hours t are there 50000 cells?
N0 = 5000k = 0.3 h⁻¹N = 50000
t = h
3.Medium
Solve y″ + 2y′ + y = 0 with y(0) = 2 and y′(0) = 2. Find y(1.5).
y″ + 2y′ + y = 0y(0) = 2y′(0) = 2
y(1.5) =
4.Medium
Solve y″ + 2y′ + y = 0 with y(0) = 3 and y′(0) = 4. Find y(2).
y″ + 2y′ + y = 0y(0) = 3y′(0) = 4
y(2) =
5.Hard
Solve y″ + 4y′ + 29y = 0 with y(0) = 3 and y′(0) = 0 (released from rest). Find y(0.5); angles in radians.
y″ + 4y′ + 29y = 0y(0) = 3y′(0) = 0
y(0.5) =
6.Hard
A system obeys y″ + 2y′ + 17y = 85 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(1.5); angles in radians.
y″ + 2y′ + 17y = 85y(0) = 0y′(0) = 0
y(1.5) =
Answer key
- 1. ζ = 0.25
- 2. t = 7.675 h
- 3. y(1.5) = 1.785
- 4. y(2) = 2.301
- 5. y(0.5) = −0.62
- 6. y(1.5) = 4.007
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