For the equation y″ + 4y′ + 3y = 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″ + 4y′ + 3y = 0
r =
2.Easy
A radioactive tracer has a half-life of 17 days. A sample initially contains 120 mg. The decay follows dm/dt = −k·m. How much m remains after 38 days?
m0 = 120 mgt½ = 17 dt = 38 d
m = mg
3.Medium
Solve y″ + 8y′ + 16y = 0 with y(0) = 1 and y′(0) = -2. Find y(1).
y″ + 8y′ + 16y = 0y(0) = 1y′(0) = -2
y(1) =
4.Medium
Solve y″ + 4y′ + 4y = 0 with y(0) = 5 and y′(0) = -1. Find y(2).
y″ + 4y′ + 4y = 0y(0) = 5y′(0) = -1
y(2) =
5.Hard
A system obeys y″ + 4y′ + 20y = 20 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(0.75); angles in radians.
y″ + 4y′ + 20y = 20y(0) = 0y′(0) = 0
y(0.75) =
6.Hard
Solve y″ + 4y′ + 8y = 0 with y(0) = 5 and y′(0) = 0 (released from rest). Find y(0.25); angles in radians.
y″ + 4y′ + 8y = 0y(0) = 5y′(0) = 0
y(0.25) =
Answer key
- 1. r = −1
- 2. m = 25.49 mg
- 3. y(1) = 0.05495
- 4. y(2) = 0.4213
- 5. y(0.75) = 1.205
- 6. y(0.25) = 4.115
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