A radioactive tracer has a half-life of 20 days. A sample initially contains 20 mg. The decay follows dm/dt = −k·m. How much m remains after 10 days?
Differential equations worksheet with answers
1.Easy
m0 = 20 mgt½ = 20 dt = 10 d
m = mg
2.Easy
A radioactive tracer has a half-life of 21 days. A sample initially contains 50 mg. The decay follows dm/dt = −k·m. How much m remains after 16 days?
m0 = 50 mgt½ = 21 dt = 16 d
m = mg
3.Medium
Solve y″ + 7y′ + 12y = 0 with y(0) = 3 and y′(0) = 1. Find y(0.5).
y″ + 7y′ + 12y = 0y(0) = 3y′(0) = 1
y(0.5) =
4.Medium
A forged steel part at 460 °C is left to cool in a workshop at 24 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). With k = 0.03 min⁻¹, find its temperature T after 21 min.
T0 = 460 °CTa = 24 °Ck = 0.03 min⁻¹t = 21 min
T = °C
5.Hard
Solve y′ + y = 4e−0.5t with y(0) = 3. Find y(2).
y′ + y = 4e−0.5ty(0) = 3
y(2) =
6.Hard
Solve the initial value problem y′ + 3y/x = 2x for x > 0, with y(1) = −3. Find y(2).
y′ + 3y/x = 2xy(1) = −3
y(2) =
Answer key
- 1. m = 14.14 mg
- 2. m = 29.49 mg
- 3. y(0.5) = 1.547
- 4. T = 256.2 °C
- 5. y(2) = 2.266
- 6. y(2) = 1.175
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