Quiz

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Quiz 1 Solutions
PHYS 2211 A SUMMER 2005
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1. (10 Points) Lois Lane trips and falls off t
he top of a 120-meter tall building. Superman
arrives on the top of the building 1.2 s after
Lois falls. What is the magnitude of the minimum
initial downward velocity Superman must have if
he is to save Lois before she hits the street?
(a) 16 m/s (b) 14 m/s
(c) 12 m/s (d) 10 m/s
(e) 9.6 m/s  
Solution Assume that down is the positive
direction and the top of the building is y 0.
How long does Superman have to save Lois?
How long after she falls will Lois hit the ground?
How much time does Superman have to get to street
level and save Lois?
What initial speed must Superman have to reach
the street in a time of 3.746 sec?
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2. (10 Points) Two cars each move with a const
ant acceleration. Starting from rest Car A
finishes a 1.0-km course at a speed of 60 m/s.
Car B finishes the same course at a speed of 55
m/s. What head start must the slower car be
given if it is to just beat the faster car in a
1.0-km race? (a) 83 m (b) 98 m
(c) 160 m (d) 180 m
(e) 120 m
Find the acceleration of each car.
How much time does it take for the faster car to
travel the 1000 meters?
How far can the slower car travel in the time it
takes the faster car to finish?
Slower car needs a head start of 159.4 meters if
he is to win.
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3. (10 Points) Jet fighter planes launched fro
m aircraft carriers are accelerated from rest to
a takeoff speed of 60 m/s in a distance of only
40 meters. What constant acceleration is
necessary to launch a plane? (a) 90 m/s2
(b) 60 m/s2 (c) 45 m/s2
(d) 23 m/s2 (e) 45 m/s2
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4. (5 Points) An object constrained to move al
ong the x-axis passes through the origin at time
t 0. The velocity of the object is a function
of time given by
What is the average velocity of the object for
the time period ? (a) 7.0 m/s (b) -2.0
m/s (c) -8.1 m/s (d)
6.4 m/s (e) 3.6 m/s
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5. (5 Points) What is the average speed of the
object in the previous problem for the same time
interval? (a) 2.0 m/s (b) 7.0 m/s
(c) 3.6 m/s (d) 9.2 m/s
(e) 8.1 m/s
Factoring the velocity expression reveals that it
is zero at t 4 sec and again at t 7 sec. In
the period 4 The total distance traveled is the distance
travel from t 0 to t 4 sec plus the distance
traveled backward from t 4 to t 6 sec.
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6. (5 Points) A rocket, initially at rest, is
fired vertically with an upward acceleration of
10 m/s2. At an altitude of 500 m, the engine of
the rocket cuts off. What is the maximum
altitude it achieves? (a) 2.0 km (b)
750 m (c) 980 m (d)
1.0 km (e) 1.2 km  
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7. (5 points) How much time elapses between the
time that the rockets engine cuts off and the
rocket strikes the ground? (a) 25 sec
(b) 21 sec (c) 4.2 sec
(d) 9.5 sec (e) 28 sec
The root 4.154 is extraneous.
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8. (10 points) A particle constrained to move al
ong the x-axis was initially at the origin. At a
later time it has a positive displacement, a
negative velocity, and a negative acceleration.
Which of the following statements is correct for
this particle? The particle's speed is decreasing
, and the particle is approaching the origin.
(b) The particle's speed is decreasing, and
the particle is moving away from the origin.
(c) The particle's speed is increasing, and the
particle is moving away from the origin.
(d) The particle's speed is increasing, and the
particle is approaching the origin.
(e) None of the above is true.  
If the displacement is positive and the velocity
is negative then the displacement is becoming
less positive and the particle is approaching the
origin. If the velocity is negative and the acc
eleration is also negative then the velocity is
becoming more negative in time and the magnitude
of the velocity is increasing, The speed is
therefore increasing.
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9. (10 points) A ball thrown vertically upward p
asses a 2.0-meter tall window in a time of 0.50
sec. What was the speed of the ball at the top of
the window? (a) 6.4 m/s (b) 4.0 m/s
(c) 1.8 m/s (d) 0.75 m/s
(e) 1.5 m/s
This is exactly the same as the Flower pot falls
past a window in the homework.
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10. (10 points) The graph below shows the positi
on of an object as a function of time. At what
point does the object achieve its greatest
speed?
The slope is most steep at point C.
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11. (10 points) A certain suburban lot
is rectangular. It is 500 meters wide east to
west and 300 meters wide north to south. The
house is built in the exact center of the lot.
The homeowner stands at the southwest corner of
his lot and starts walking east at 2.0 m/s. At
the instant that she starts, at what rate is she
approaching the house? 1.0 m/s (b) 2.0 m/s
(c) 1.7 m/s (d) 0.75 m/s
(e) 1.4 m/s
A diagonal across the lot through the house makes
an angle of 30.96º with the southern border of
the lot. We seek to know the component of the
velocity in the direction of this diagonal.
Rotate the coordinate system.
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12. (10 points) Which of the following correspon
ds to the
Figure?