A quantity grows according to dy/dt = k·y with k > 0. It is 50 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) = 50y(12) = 180
k = h⁻¹
2.Easy
For the equation y″ + 7y′ + 12y = 0, find the root r of the characteristic equation that is closest to zero. It sets how slowly the solution dies out.
y″ + 7y′ + 12y = 0
r =
3.Medium
A cup of coffee at 82 °C is left in a room at 19 °C. After 10 min its temperature is 47 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). How long after the start, t, does it take to reach 29 °C?
T0 = 82 °CTa = 19 °CT(10) = 47 °CT = 29 °C
t = min
4.Medium
Solve y″ + 6y′ + 8y = 0 with y(0) = 5 and y′(0) = 0. Find y(0.5).
y″ + 6y′ + 8y = 0y(0) = 5y′(0) = 0
y(0.5) =
5.Hard
Solve y″ + y′ + 16.25y = 0 with y(0) = 3 and y′(0) = 0 (released from rest). Find y(1); angles in radians.
y″ + y′ + 16.25y = 0y(0) = 3y′(0) = 0
y(1) =
6.Hard
A system obeys y″ + 4y′ + 8y = 8 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find the peak value ymax of its step response.
y″ + 4y′ + 8y = 8y(0) = 0y′(0) = 0
ymax =
Answer key
- 1. k = 0.1067 h⁻¹
- 2. r = −3
- 3. t = 22.7 min
- 4. y(0.5) = 3.002
- 5. y(1) = −1.361
- 6. ymax = 1.043
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