A quantity grows according to dy/dt = k·y with k > 0. It is 120 at t = 0 and 216 at t = 12 h. Find the rate constant k in h⁻¹.
Differential equations worksheet with answers
1.Easy
y(0) = 120y(12) = 216
k = h⁻¹
2.Easy
A mass–spring–damper is described by y″ + 10y′ + 100y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
y″ + 10y′ + 100y = 0
ζ =
3.Medium
A forged steel part at 340 °C is left to cool in a workshop at 24 °C. After 59 min its temperature is 199 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
T0 = 340 °CTa = 24 °CT(59) = 199 °C
k = min⁻¹
4.Medium
Solve y″ + 7y′ + 12y = 0 with y(0) = 4 and y′(0) = 0. Find y(1).
y″ + 7y′ + 12y = 0y(0) = 4y′(0) = 0
y(1) =
5.Hard
Solve y′ + y = 5e−0.5t with y(0) = 0. Find y(1).
y′ + y = 5e−0.5ty(0) = 0
y(1) =
6.Hard
Solve y″ + 2y′ + 26y = 0 with y(0) = 5 and y′(0) = 0 (released from rest). Find y(0.75); angles in radians.
y″ + 2y′ + 26y = 0y(0) = 5y′(0) = 0
y(0.75) =
Answer key
- 1. k = 0.04898 h⁻¹
- 2. ζ = 0.5
- 3. k = 0.01002 min⁻¹
- 4. y(1) = 0.5768
- 5. y(1) = 2.387
- 6. y(0.75) = −2.208
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