A mass–spring–damper is described by y″ + 7.2y′ + 9y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
A radioactive tracer has a half-life of 29 days. A sample initially contains 80 mg. The decay follows dm/dt = −k·m. How much m remains after 99 days?
A forged steel part at 380 °C is left to cool in a workshop at 28 °C. After 13 min its temperature is 237 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
Solve y″ + 6y′ + 5y = 0 with y(0) = 5 and y′(0) = -2. Find y(0.5).
A system obeys y″ + y′ + 4.25y = 8.5 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find the peak value ymax of its step response.
A system obeys y″ + 3y′ + 27.25y = 136.3 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find the peak value ymax of its step response.
Answer key
- 1. ζ = 1.2
- 2. m = 7.506 mg
- 3. k = 0.0401 min⁻¹
- 4. y(0.5) = 3.426
- 5. ymax = 2.912
- 6. ymax = 6.948
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