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categoryهندسة ميكانيكية
schoolبكالوريوس
event_available2026-07-13
السؤال
Transcribed Image Text:
The suspension of a modified baby bouncer is modelled by a model
spring AP with stiffness k₁ and a model damper BP with damping
coefficient r. The seat is tethered to the ground, and this tether is
modelled by a second model spring PC with stiffness k₂. Model the
combination of baby and seat as a particle of mass m at a point P that is
a distance r above floor level.
The bouncer is suspended from a fixed support at a height h above the
floor. The suspending spring has natural length 11, while the tethering
spring has natural length l₂. Take the origin at floor level, with the unit
vector i pointing upwards, as shown in the following diagram.
ki, 1
h
P
AB
-000000
k2, 2
000000
(a) Draw a force diagram showing all forces acting on the particle P.
(b) Copy and complete the following table, and hence write down the
force on particle P due to each model spring. The notation is the
same as that used in the unit.
Spring Spring Natural Extension Stiffness
H
length
length
AP
11
CP
12
k1
k₂
(c) Copy and complete the following table, and hence write down the
force on particle P due to the model damper. The notation is the
same as that used in the unit.
Damper Rate of change Damping
R
length
of length
constant
r
(d) Model the remaining forces acting on the particle P, and hence show
that the equation of motion of the mass is
mi+ri+ (k₁+k2)x = k₁(h-l₁) + k2l2-mg.
(e) In SI units, suppose that m = 10, k₁ = 150, k₂ = 100, r = 20, h = 1.5,
₁ = 0.5 and 12 = 0.25. Determine the natural angular frequency of
the system to two decimal places.
Using the same data, calculate the damping ratio for this mechanical
system to two decimal places, and hence state whether the system
undergoes strong, weak or critical damping. Comment on whether
this damping is appropriate for a baby bouncer.
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