A mass–spring–damper is described by y″ + 3.2y′ + 64y = 0. Compare it with y″ + 2ζωny′ + ωn²y = 0 and find the damping ratio ζ.
Differential equations worksheet with answers
1.Easy
y″ + 3.2y′ + 64y = 0
ζ =
2.Easy
A radioactive tracer has a half-life of 9 days. A sample initially contains 80 mg. The decay follows dm/dt = −k·m. How much m remains after 22 days?
m0 = 80 mgt½ = 9 dt = 22 d
m = mg
3.Medium
A cup of coffee at 89 °C is left in a room at 20 °C. It follows Newton's law of cooling, dT/dt = −k·(T − Tₐ). With k = 0.04 min⁻¹, find its temperature T after 7 min.
T0 = 89 °CTa = 20 °Ck = 0.04 min⁻¹t = 7 min
T = °C
4.Medium
Solve y″ + 5y′ + 6y = 0 with y(0) = 4 and y′(0) = 2. Find y(1.5).
y″ + 5y′ + 6y = 0y(0) = 4y′(0) = 2
y(1.5) =
5.Hard
A system obeys y″ + 4y′ + 8y = 8 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find y(0.25); angles in radians.
y″ + 4y′ + 8y = 8y(0) = 0y′(0) = 0
y(0.25) =
6.Hard
A system obeys y″ + 4y′ + 20y = 40 for t ≥ 0, starting from rest: y(0) = 0, y′(0) = 0. Find the peak value ymax of its step response.
y″ + 4y′ + 20y = 40y(0) = 0y′(0) = 0
ymax =
Answer key
- 1. ζ = 0.2
- 2. m = 14.7 mg
- 3. T = 72.15 °C
- 4. y(1.5) = 0.5859
- 5. y(0.25) = 0.1769
- 6. ymax = 2.416
Full step-by-step solutions: practise this topic on examproblems.com.