A quantity decays according to dy/dt = −k·y with k > 0. It is 100 at t = 0 and 55 at t = 10 h. Find the rate constant k in h⁻¹.
Differential equations worksheet with answers
A mass–spring–damper is described by y″ + 19.2y′ + 64y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
A can of soda at 5 °C is taken out of the fridge into a room at 27 °C. After 6 min its temperature is 10 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
A can of soda at 4 °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 = 0.07 min⁻¹, find its temperature T after 22 min.
Solve y″ + 2y′ + 10y = 0 with y(0) = 10 and y′(0) = 0 (released from rest). Find y(0.25); angles in radians.
Solve y″ + 4y′ + 20y = 0 with y(0) = 3 and y′(0) = 0 (released from rest). Find y(1.5); angles in radians.
Answer key
- 1. k = 0.05978 h⁻¹
- 2. ζ = 1.2
- 3. k = 0.04297 min⁻¹
- 4. T = 18.93 °C
- 5. y(0.25) = 7.468
- 6. y(1.5) = 0.1225
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