valdez (vv689) – Homework 03 – florin – (58140)
1
This
printout
should
have
12
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0 points
An object is shot vertically upward into the
air with a positive initial velocity.
What correctly describes the velocity and
acceleration of the object at its maximum
elevation?
Velocity
Acceleration
1.
positive
positive
2.
zero
zero
3.
positive
negative
4.
negative
negative
5.
zero
negative
correct
Explanation:
At the maximum elevation, the vertical ve
locity is zero.
The acceleration is due to
gravity, which always acts down.
002
10.0 points
A subway train starting from rest leaves a
station with a constant acceleration.
At the
end of 7
.
02 s, it is moving at 20
.
0772 m
/
s.
What is the train’s displacement in the first
5
.
2299 s of motion?
Correct answer: 39
.
1132 m.
Explanation:
Let :
Δ
t
= 7
.
02 s
,
Δ
v
= 20
.
0772 m
/
s
,
and
t
1
= 5
.
2299 s
.
a
=
Δ
v
Δ
t
, so the displacement is
s
=
1
2
a t
2
=
1
2
Δ
v
Δ
t
t
2
=
1
2
20
.
0772 m
/
s
7
.
02 s
(5
.
2299 s)
2
=
39
.
1132 m
.
003
10.0 points
The acceleration of gravity is 10 m
/
s
2
.
If there were no air resistance, with what
speed would drops hit the Earth if they fell
from a cloud 1705 m above the Earth’s sur
face?
Correct answer: 184
.
662 m
/
s.
Explanation:
Drops would be in free fall and accelerate
at 10 m
/
s
2
.
We need to find the time of fall.
From
d
=
1
2
g t
2
,
the time is
t
=
radicalBigg
2
d
g
=
radicalBigg
2 (1705 m)
10 m
/
s
2
= 18
.
4662 s
.
gain in speed =
g t
= (10 m
/
s
2
) (18
.
4662 s)
=
184
.
662 m
/
s
.
004
10.0 points
The diagram describes the acceleration
vs
time behavior for a car moving in the
x

direction.
a
P
Q
t
0
At the point
Q
, the car is moving
1.
with a decreasing speed.
2.
with a constant speed.
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valdez (vv689) – Homework 03 – florin – (58140)
2
3.
with an increasing speed.
correct
Explanation:
a
=
d v
dt
.
As long as the acceleration is
positive the velocity is always increasing.
005
10.0 points
A car is moving at constant speed on the
freeway. The driver sees a patrol car at time
t
1
and rapidly slows down by around 10 miles
per hour. After continuing at this speed for a
few minutes, the driver at time
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 Spring '10
 SVHETS
 Acceleration, Velocity, m/s, Valdez

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