A quantity grows according to dy/dt = k·y with k > 0. It is 200 at t = 0 and 380 at t = 9 h. Find the rate constant k in h⁻¹.
Differential equations worksheet with answers
1.Easy
y(0) = 200y(9) = 380
k = h⁻¹
2.Easy
A mass–spring–damper is described by y″ + 2y′ + 100y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
y″ + 2y′ + 100y = 0
ζ =
3.Medium
A can of soda at 6 °C is taken out of the fridge into a room at 22 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). With k = 0.1 min⁻¹, find its temperature T after 24 min.
T0 = 6 °CTa = 22 °Ck = 0.1 min⁻¹t = 24 min
T = °C
4.Medium
Solve y″ + 2y′ + y = 0 with y(0) = 1 and y′(0) = 2. Find y(1.5).
y″ + 2y′ + y = 0y(0) = 1y′(0) = 2
y(1.5) =
5.Hard
Solve y′ + y = 10e−0.5t with y(0) = 2. Find y(1.5).
y′ + y = 10e−0.5ty(0) = 2
y(1.5) =
6.Hard
A system obeys y″ + y′ + 16.25y = 32.5 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(0.25); angles in radians.
y″ + y′ + 16.25y = 32.5y(0) = 0y′(0) = 0
y(0.25) =
Answer key
- 1. k = 0.07132 h⁻¹
- 2. ζ = 0.1
- 3. T = 20.55 °C
- 4. y(1.5) = 1.227
- 5. y(1.5) = 5.431
- 6. y(0.25) = 0.8607
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