-
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CA
梁柱
一截面積是原來的兩倍
22. Two girders are made of the same material. Girder A is twice as long as girder B and
Bo
DE
C
B³
has a cross-sectional area that is twice as great. The ratio of the mass density of girder
A to the mass density of girder B is:
質量密度
A) 4
B) 2
C)
1
D)
1/2
E) 1/4
29. During a short interval of time the speed v in m/s of an automobile is given by v=at² +
bt³, where the time t is in seconds. The units of a and b are respectively:
A) m-s²; m-s4
s³/m; s4/m
dv=at+bt²
B)
C)
m/s²; m/s³
D)
m/s³; m/s4
E) m/s4; m/s5
34. The position y of a particle moving along the y axis depends on the time t according to
the equation
B)
C)
D)
E)
質固定,体2倍
#%#
40. The coordinate of an object is given as a function of time by x = 7t-31², where x is in
meters and t is in seconds. Its average velocity over the interval from t = 0 to t = 2 s is:
A) 5 m/s
X₂=0, X₁₂=14-12=2
B) -5 m/s
11 m/s
C)
D) -11 m/s
(2-0)/2=1
E) -14.5 m/s
41. The coordinate of a particle in meters is given by x(t) = 16t-3.01³, where the time t is in
seconds. The particle is momentarily at rest at t =
A) 0.75 s
A
y = at -bt². The dimensions of the quantities a and b are respectively:
A) L²/T, L³/T2
B)
L/T², L²/T
C)
L/T, L/T²
D)
L³/T, T²/L
E) none of these
1.3 s
5.3 s
7.3 s
9.3 s
V(t) = 16-9+²
=- [9t²-16)
=-(3t+4) 13t-4)
=+= 0.75
45. The velocity of an object is given as a function of time by v = 4t-312, where v is in m/s
and t is in seconds. Its average velocity over the interval from t=0 to t=2 s:
A) is 0
B)
is -2 m/s
C)
is 2 m/s
D)
is -4 m/s
E) cannot be calculated unless the initial position is given
49. A particle moves along the x axis according to the equation x = 61² where x is in meters
and t is in seconds. Therefore:
E
B)
C)
D)
E)
A) the acceleration of the particle is 6 m/s²
t cannot be negative
the particle follows a parabolic path
each second the velocity of the particle changes by 9.8 m/s
none of the above
