The Medical College - Page 40
89.
A centrifuge starts from rest and reaches a
final
angular speed of 57,300 rev/min in 2
minutes.
(Recall that 1 rev = 2
radians.) What is the
angular acceleration of the
centrifuge?
A.
50 rad/sec
2
C.
3000 rad/sec
2
B.
32 rad/sec
2
D.
12 rad/sec
2
90.
A 4 kg block is initially moving at 5 m/sec
when
the applied force is removed, and the
block
slides to rest on a rough floor with a
coefficient
of friction of 0.4. How much work is done by
the
friction force in stopping the
block?
A.
400 joules
C.
100 joules
B.
50 joules
D.
220 joules
91.
A woman can see clearly only those objects
that
are no more than 50 cm from her eyes. (Her
"far
point" is at 0.5 m.) She needs glasses with
a
focal length of –0.5 m. State the power of
this
lens in Diopters and whether it is a
converging
lens or a diverging lens.
A.
–2.0 D, converging
B.
–2.0 D, diverging
C.
–0.5 D, converging
D.
–0.5 D, diverging
92.
Forces of 2 newtons act for 4 seconds on
masses
of 3 kg and 6 kg, which are initially at rest
on
frictionless surfaces. What are the
respective
momenta of the 3 kg and 6 kg masses at the
end
of the 4 sec periods.
A.
6 and 12 kg-m/sec
B.
8 and 8 kg-m/sec
C.
12 and 6 kg-m/sec
D.
12 and 24 kg-m/sec
93.
The isotope 29Cu
64 is unusual in that
it can decay
by
, –, and + emission. (The + is a positron
or positive electron, while the
– is the
usual
electron.) What is the resulting nuclide for
each
case? (
, –, +)
A.
Ni
63,
Co64,
Fe63
C.
Cu
64,
Zn64,
Ni64
B.
Ni
64,
Zn63,
Co64
D.
Ni
64,
Cu64,
Zn64
94.
The index of refraction of water is
nw =
1.33.
The speed of light in a certain substance is
83%
of its value in water. What is the index of
refrac-
tion, nu, of this substance?
A.
1.6
C.
1.1
B.
1.8
D.
2.1
95.
The electrical repulsive force between
two
charges of 1 microcoulomb and 2
micro-
coulombs is 0.54 N. The separation
between
them is then decreased to one-half as
much.
What is the new force between the
charges?
A.
0.27 N
C.
1.08 N
B.
2.16 N
D.
0.81 N
Passage V (Questions 96–105)
A set of laboratory experiments designed to
physi-
cally involve the students is planned for a
high school
physics course. They are to verify Newton's
laws of
motion and the conservation laws for linear and
angu-
lar momentum. A pair of low carts on which the
stu-
dent sits are fitted with two complete
skateboard wheel
sets each. A laser beam and photogate can
measure the
velocities of such large objects using a
commercial
computer timing system. The forces required are
mea-
sured with calibrated spring scales. The
experiments
are performed in the gymnasium to make use of
its
large smooth floor area. The instructor has
devised a
pulley and falling mass system to provide the
constant
forces to accelerate the cart student systems,
but most
of the time she has the student provide the
accelerating
forces by walking backward while keeping the
force
reading constant on a spring scale. The
experience
of providing a constant force while
accelerating gives
the pulling student a "feel" for the real
meaning of
acceleration.
96.
A student practices until he can pull a
classmate
at constant speed to just overcome friction.
This
requires a force of 9 N when the mass of
cart-
student is 90 kg. The student then
accelerates
the cart-student by pulling with a constant
force
of 18 N. What is the measured
acceleration?
A.
0.1 m/sec
2
C.
1.2 m/sec
2
B.
0.8 m/sec
2
D.
4.2 m/sec
2
97.
Two students of different masses sit on
carts
close together. They push off from each
other
and their velocities are measured just after
they
separate. The 60 kg student-cart has a speed
of
1.2 m/sec. The other student-cart has an
opposite
speed of 0.8 m/sec. What is the mass of the
sec-
ond student-cart?
A.
40 kg
C.
110 kg
B.
90 kg
D.
120 kg
98.
A student-cart of mass 80 kg has an initial
speed
through a photogate of 2 m/sec. The
frictional
forces bring the cart to rest after it travels
8 m.
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