A quantity grows according to dy/dt = k·y with k > 0. It is 100 at t = 0 and 180 at t = 12 h. Find the rate constant k in h⁻¹.
Differential equations worksheet with answers
1.Easy
y(0) = 100y(12) = 180
k = h⁻¹
2.Easy
A radioactive tracer has a half-life of 29 days. A sample initially contains 50 mg. The decay follows dm/dt = −k·m. How much m remains after 84 days?
m0 = 50 mgt½ = 29 dt = 84 d
m = mg
3.Medium
Solve y″ + 5y′ + 4y = 0 with y(0) = 1 and y′(0) = 6. Find y(2).
y″ + 5y′ + 4y = 0y(0) = 1y′(0) = 6
y(2) =
4.Medium
Solve y″ + 7y′ + 12y = 0 with y(0) = 3 and y′(0) = 2. Find y(2).
y″ + 7y′ + 12y = 0y(0) = 3y′(0) = 2
y(2) =
5.Hard
Solve the initial value problem y′ + 2y/x = 2x for x > 0, with y(1) = 0. Find y(3).
y′ + 2y/x = 2xy(1) = 0
y(3) =
6.Hard
A system obeys y″ + 3y′ + 18.25y = 91.25 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(0.5); angles in radians.
y″ + 3y′ + 18.25y = 91.25y(0) = 0y′(0) = 0
y(0.5) =
Answer key
- 1. k = 0.04898 h⁻¹
- 2. m = 6.715 mg
- 3. y(2) = 0.4503
- 4. y(2) = 0.03101
- 5. y(3) = 4.444
- 6. y(0.5) = 5.178
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