A quantity grows according to dy/dt = k·y with k > 0. It is 200 at t = 0 and 400 at t = 9 h. Find the rate constant k in h⁻¹.
Differential equations worksheet with answers
1.Easy
y(0) = 200y(9) = 400
k = h⁻¹
2.Easy
A radioactive tracer has a half-life of 25 days. A sample initially contains 10 mg. The decay follows dm/dt = −k·m. How much m remains after 44 days?
m0 = 10 mgt½ = 25 dt = 44 d
m = mg
3.Medium
Solve y″ + 7y′ + 10y = 0 with y(0) = 2 and y′(0) = 4. Find y(1.5).
y″ + 7y′ + 10y = 0y(0) = 2y′(0) = 4
y(1.5) =
4.Medium
Solve y″ + 4y′ + 4y = 0 with y(0) = 2 and y′(0) = -2. Find y(1.5).
y″ + 4y′ + 4y = 0y(0) = 2y′(0) = -2
y(1.5) =
5.Hard
A system obeys y″ + 2y′ + 5y = 50 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(0.5); angles in radians.
y″ + 2y′ + 5y = 50y(0) = 0y′(0) = 0
y(0.5) =
6.Hard
Solve the initial value problem y′ + y/x = 4x2 for x > 0, with y(1) = 0. Find y(2).
y′ + y/x = 4x2y(1) = 0
y(2) =
Answer key
- 1. k = 0.07702 h⁻¹
- 2. m = 2.952 mg
- 3. y(1.5) = 0.2309
- 4. y(1.5) = 0.2489
- 5. y(0.5) = 4.171
- 6. y(2) = 7.5
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