A mass–spring–damper is described by y″ + 2.4y′ + 36y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
1.Easy
y″ + 2.4y′ + 36y = 0
ζ =
2.Easy
A bacterial culture starts with 500 cells and grows according to dN/dt = k·N with k = 0.06 h⁻¹. How many cells N are there after 20 h?
N0 = 500k = 0.06 h⁻¹t = 20 h
N =
3.Medium
Solve y″ + 3y′ + 2y = 0 with y(0) = 2 and y′(0) = 1. Find y(2).
y″ + 3y′ + 2y = 0y(0) = 2y′(0) = 1
y(2) =
4.Medium
A cup of coffee at 94 °C is left in a room at 19 °C. After 21 min its temperature is 26 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
T0 = 94 °CTa = 19 °CT(21) = 26 °C
k = min⁻¹
5.Hard
Solve y″ + 2y′ + 26y = 0 with y(0) = 5 and y′(0) = 0 (released from rest). Find y(0.25); angles in radians.
y″ + 2y′ + 26y = 0y(0) = 5y′(0) = 0
y(0.25) =
6.Hard
A system obeys y″ + 4y′ + 8y = 80 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(1.5); angles in radians.
y″ + 4y′ + 8y = 80y(0) = 0y′(0) = 0
y(1.5) =
Answer key
- 1. ζ = 0.2
- 2. N = 1660
- 3. y(2) = 0.6217
- 4. k = 0.1129 min⁻¹
- 5. y(0.25) = 1.967
- 6. y(1.5) = 10.42
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