A mass–spring–damper is described by y″ + 3.2y′ + 16y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
1.Easy
y″ + 3.2y′ + 16y = 0
ζ =
2.Easy
A radioactive tracer has a half-life of 20 days. A sample initially contains 120 mg. The decay follows dm/dt = −k·m. How much m remains after 54 days?
m0 = 120 mgt½ = 20 dt = 54 d
m = mg
3.Medium
A can of soda at 3 °C is taken out of the fridge into a room at 29 °C. After 28 min its temperature is 24 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). Find the constant k in min⁻¹.
T0 = 3 °CTa = 29 °CT(28) = 24 °C
k = min⁻¹
4.Medium
Solve y″ + 2y′ + y = 0 with y(0) = 3 and y′(0) = 1. Find y(1.5).
y″ + 2y′ + y = 0y(0) = 3y′(0) = 1
y(1.5) =
5.Hard
Solve y″ + y′ + 9.25y = 0 with y(0) = 2 and y′(0) = 0 (released from rest). Find y(0.75); angles in radians.
y″ + y′ + 9.25y = 0y(0) = 2y′(0) = 0
y(0.75) =
6.Hard
A system obeys y″ + 2y′ + 5y = 25 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find the peak value ymax of its step response.
y″ + 2y′ + 5y = 25y(0) = 0y′(0) = 0
ymax =
Answer key
- 1. ζ = 0.4
- 2. m = 18.47 mg
- 3. k = 0.05888 min⁻¹
- 4. y(1.5) = 2.008
- 5. y(0.75) = −0.6852
- 6. ymax = 6.039
Full step-by-step solutions: practise this topic on examproblems.com.