A mass–spring–damper is described by y″ + 3.6y′ + 9y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
1.Easy
y″ + 3.6y′ + 9y = 0
ζ =
2.Easy
A radioactive tracer has a half-life of 29 days. A sample initially contains 10 mg. The decay follows dm/dt = −k·m. How much m remains after 79 days?
m0 = 10 mgt½ = 29 dt = 79 d
m = mg
3.Medium
Solve y″ + 3y′ + 2y = 0 with y(0) = 1 and y′(0) = -2. Find y(1.5).
y″ + 3y′ + 2y = 0y(0) = 1y′(0) = -2
y(1.5) =
4.Medium
A can of soda at 6 °C is taken out of the fridge into a room at 24 °C. After 9 min its temperature is 14 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
T0 = 6 °CTa = 24 °CT(9) = 14 °C
k = min⁻¹
5.Hard
Solve y′ + y = 3e−0.5t with y(0) = 4. Find y(1).
y′ + y = 3e−0.5ty(0) = 4
y(1) =
6.Hard
Solve y″ + 4y′ + 8y = 0 with y(0) = 10 and y′(0) = 0 (released from rest). Find y(0.75); angles in radians.
y″ + 4y′ + 8y = 0y(0) = 10y′(0) = 0
y(0.75) =
Answer key
- 1. ζ = 0.6
- 2. m = 1.513 mg
- 3. y(1.5) = 0.04979
- 4. k = 0.06531 min⁻¹
- 5. y(1) = 2.903
- 6. y(0.75) = 2.384
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