For the equation y″ + 7y′ + 12y = 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″ + 7y′ + 12y = 0
r =
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 can of soda at 4 °C is taken out of the fridge into a room at 24 °C. After 5 min its temperature is 12 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). How long after the start, t, does it take to reach 17 °C?
T0 = 4 °CTa = 24 °CT(5) = 12 °CT = 17 °C
t = min
4.Medium
Solve y″ + 6y′ + 8y = 0 with y(0) = 3 and y′(0) = 0. Find y(1).
y″ + 6y′ + 8y = 0y(0) = 3y′(0) = 0
y(1) =
5.Hard
Solve the initial value problem y′ + 3y/x = 5 for x > 0, with y(1) = 1. Find y(2).
y′ + 3y/x = 5y(1) = 1
y(2) =
6.Hard
A system obeys y″ + 3y′ + 6.25y = 6.25 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(1); angles in radians.
y″ + 3y′ + 6.25y = 6.25y(0) = 0y′(0) = 0
y(1) =
Answer key
- 1. r = −3
- 2. ζ = 0.5
- 3. t = 10.28 min
- 4. y(1) = 0.7571
- 5. y(2) = 2.469
- 6. y(1) = 0.9407
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