A radioactive tracer has a half-life of 4 days. A sample initially contains 10 mg. The decay follows dm/dt = −k·m. How much m remains after 13 days?
Differential equations worksheet with answers
1.Easy
m0 = 10 mgt½ = 4 dt = 13 d
m = mg
2.Easy
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.
y″ + 6y′ + 8y = 0
r =
3.Medium
Solve y″ + 4y′ + 4y = 0 with y(0) = 3 and y′(0) = -2. Find y(0.5).
y″ + 4y′ + 4y = 0y(0) = 3y′(0) = -2
y(0.5) =
4.Medium
Solve y″ + 6y′ + 8y = 0 with y(0) = 2 and y′(0) = -2. Find y(1).
y″ + 6y′ + 8y = 0y(0) = 2y′(0) = -2
y(1) =
5.Hard
Solve the initial value problem y′ + 3y/x = 4 for x > 0, with y(1) = −2. Find y(2).
y′ + 3y/x = 4y(1) = −2
y(2) =
6.Hard
Solve y″ + 4y′ + 8y = 0 with y(0) = 1 and y′(0) = 0 (released from rest). Find y(0.25); angles in radians.
y″ + 4y′ + 8y = 0y(0) = 1y′(0) = 0
y(0.25) =
Answer key
- 1. m = 1.051 mg
- 2. r = −2
- 3. y(0.5) = 1.839
- 4. y(1) = 0.3877
- 5. y(2) = 1.625
- 6. y(0.25) = 0.8231
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