.15 A hitch-mounted bicycle rack is designed to carry up to four 30-lb bikes mounted on and strapped to two arms Gil (sec bike loads in the figure part a) The rack is attached to the vehicle at A and is assumed to be like a cant silkier beam A BCDGII (figure part b) The light of fixed segment AB is U = 10 lb. centered 9 in. from A (see figure part b) and the rest of the rack highs W2 = 40 lb. centered 19 in. from A. Segment ABCDG is a steel tube o(2 X 2 in. with a thickness I = 118 in. Segment BCDGII pivots about a bolt at B with a diameter d1 = 0.25 in. to allow access to the rear of the vehicle without removing the hitch rack. When in use, the rack is secured in an upright posit ion by a pin C(diameter o( pin d, = 5116 in.) (see phoo and figure part C). The of returning effect of the bikes on the rack is resisted by a force couple F h at BC. (a) Find the support reactions at A for the fully loaded rack. (b) Find forces in the bolt at B and the pin at C. (c) Find average shear stresses in both the bolt at Band the pin at C. (d) Find average bearing stresses o, in the bolt at B and the pin at C.
.15 A hitch-mounted bicycle rack is designed to carry up to four 30-lb bikes mounted on and strapped to two arms Gil (sec bike loads in the figure part a) The rack is attached to the vehicle at A and is assumed to be like a cant silkier beam A BCDGII (figure part b) The light of fixed segment AB is U = 10 lb. centered 9 in. from A (see figure part b) and the rest of the rack highs W2 = 40 lb. centered 19 in. from A. Segment ABCDG is a steel tube o(2 X 2 in. with a thickness I = 118 in. Segment BCDGII pivots about a bolt at B with a diameter d1 = 0.25 in. to allow access to the rear of the vehicle without removing the hitch rack. When in use, the rack is secured in an upright posit ion by a pin C(diameter o( pin d, = 5116 in.) (see phoo and figure part C). The of returning effect of the bikes on the rack is resisted by a force couple F h at BC. (a) Find the support reactions at A for the fully loaded rack. (b) Find forces in the bolt at B and the pin at C. (c) Find average shear stresses in both the bolt at Band the pin at C. (d) Find average bearing stresses o, in the bolt at B and the pin at C.
.15 A hitch-mounted bicycle rack is designed to carry up to four 30-lb bikes mounted on and strapped to two arms Gil (sec bike loads in the figure part a) The rack is attached to the vehicle at A and is assumed to be like a cant silkier beam A BCDGII (figure part b) The light of fixed segment AB is U = 10 lb. centered 9 in. from A (see figure part b) and the rest of the rack highs W2 = 40 lb. centered 19 in. from A. Segment ABCDG is a steel tube o(2 X 2 in. with a thickness I = 118 in. Segment BCDGII pivots about a bolt at B with a diameter d1 = 0.25 in. to allow access to the rear of the vehicle without removing the hitch rack. When in use, the rack is secured in an upright posit ion by a pin C(diameter o( pin d, = 5116 in.) (see phoo and figure part C). The of returning effect of the bikes on the rack is resisted by a force couple F h at BC.
(a) Find the support reactions at A for the fully loaded rack.
(b) Find forces in the bolt at B and the pin at C.
(c) Find average shear stresses in both the bolt at Band the pin at C. (d) Find average bearing stresses o, in the bolt at B and the pin at C.
Q3-B (7 Marks): A mass (m) is suspended from a spring of stiffness 4000 N/m and is
subjected to a harmonic force having an amplitude of 100 N and a frequency of 5 Hz. The
amplitude of the forced motion of the mass is observed to be 20 mm. Find the value of mass
(m).
Fig. (2)
Q3-A (8 Marks): An automobile is modeled as a single-degree-of-freedom system vibrating in
the vertical direction. It is driven along a road whose elevation varies sinusoidally. The
distance from peak to trough is 0.2 m and the distance along the road between the peaks is 35
m. If the natural frequency of the automobile is 2 Hz and the damping ratio of the shock
absorbers is 0.15, determine the amplitude of vibration of the automobile at a speed of 60
km/hour
6.18
2.
Q4(15 Marks): The motor-pump system shown in Fig. 4. is modeled as a rigid bar of mass
m=50 kg and mass moment of inertia Jo=100 kg-m. The foundation of the system can be
replaced by two springs of stiffness k=500 N/m and k₂-200 N/m and L=1 m. Determine
the natural frequencies of the system.
Motor,
Fig. (4)
1
6(1)
Pump
C.G.
x(1)
x₁(1)
Base
(a)
Foundation
(b)
C.G. m, Jo
x2(1)
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