For the equation y″ + 5y′ + 4y = 0, find the root r of the characteristic equation that is closest to zero. It sets how slowly the solution dies out.
Differential equations worksheet with answers
A mass–spring–damper is described by y″ + 1.6y′ + 4y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
A can of soda at 6 °C is taken out of the fridge into a room at 23 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). With k = 0.08 min⁻¹, find its temperature T after 23 min.
A can of soda at 5 °C is taken out of the fridge into a room at 23 °C. After 28 min its temperature is 17 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
A system obeys y″ + y′ + 4.25y = 8.5 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(1.5); angles in radians.
Solve the initial value problem y′ + 3y/x = x2 for x > 0, with y(1) = −2. Find y(3).
Answer key
- 1. r = −1
- 2. ζ = 0.4
- 3. T = 20.3 °C
- 4. k = 0.03924 min⁻¹
- 5. y(1.5) = 2.902
- 6. y(3) = 4.42
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