A quantity grows according to dy/dt = k·y with k > 0. It is 200 at t = 0 and 780 at t = 3 h. Find the rate constant k in h⁻¹.
Differential equations worksheet with answers
1.Easy
y(0) = 200y(3) = 780
k = h⁻¹
2.Easy
For the equation y″ + 7y′ + 6y = 0, find the root r of the characteristic equation that is closest to zero. It sets how slowly the solution dies out.
y″ + 7y′ + 6y = 0
r =
3.Medium
A forged steel part at 460 °C is left to cool in a workshop at 27 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). With k = 0.05 min⁻¹, find its temperature T after 47 min.
T0 = 460 °CTa = 27 °Ck = 0.05 min⁻¹t = 47 min
T = °C
4.Medium
Solve y″ + 7y′ + 10y = 0 with y(0) = 2 and y′(0) = -2. Find y(1).
y″ + 7y′ + 10y = 0y(0) = 2y′(0) = -2
y(1) =
5.Hard
A system obeys y″ + 4y′ + 8y = 16 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(1); angles in radians.
y″ + 4y′ + 8y = 16y(0) = 0y′(0) = 0
y(1) =
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(0.75); angles in radians.
y″ + 3y′ + 18.25y = 91.25y(0) = 0y′(0) = 0
y(0.75) =
Answer key
- 1. k = 0.4537 h⁻¹
- 2. r = −1
- 3. T = 68.29 °C
- 4. y(1) = 0.3564
- 5. y(1) = 1.867
- 6. y(0.75) = 6.521
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