For the equation y″ + 6y′ + 8y = 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
1.Easy
y″ + 6y′ + 8y = 0
r =
2.Easy
A quantity decays according to dy/dt = −k·y with k > 0. It is 200 at t = 0 and 130 at t = 9 h. Find the rate constant k in h⁻¹.
y(0) = 200y(9) = 130
k = h⁻¹
3.Medium
A cup of coffee at 83 °C is left in a room at 19 °C. After 11 min its temperature is 52 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
T0 = 83 °CTa = 19 °CT(11) = 52 °C
k = min⁻¹
4.Medium
Solve y″ + 8y′ + 15y = 0 with y(0) = 2 and y′(0) = 6. Find y(1).
y″ + 8y′ + 15y = 0y(0) = 2y′(0) = 6
y(1) =
5.Hard
A system obeys y″ + y′ + 4.25y = 4.25 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(0.5); angles in radians.
y″ + y′ + 4.25y = 4.25y(0) = 0y′(0) = 0
y(0.5) =
6.Hard
A system obeys y″ + 2y′ + 17y = 170 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find the peak value ymax of its step response.
y″ + 2y′ + 17y = 170y(0) = 0y′(0) = 0
ymax =
Answer key
- 1. r = −2
- 2. k = 0.04786 h⁻¹
- 3. k = 0.06022 min⁻¹
- 4. y(1) = 0.3579
- 5. y(0.5) = 0.4154
- 6. ymax = 14.56
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