8
Engineering Physics 1 (Phys. 213)
Exam 1 SOLUTION, Feb. 8
th
, 2008 (O’Shea)
Name
__________________________________
Instructions: Please Read!
This is a closed book, closed notes exam. This exam contains multiplechoice questions
and problems.
For each multiplechoice question, circle the letter of the best response.
For problems, you need to show your work in a professional manner and write the final
numerical answer with the proper unit in the space shown. Numerical answers without
supporting calculations will receive zero credit. Partial credit is available only if your
work is clear.
1.
Academic honesty statement.
This exam will NOT be marked unless you sign the academic honesty statement below.
Your signature indicates that you have
read
,
understood
, and
complied
with the
meaning of this statement.
On my honor as a student I have neither
given nor received unauthorized aid on
this assignment.
Sign your name:__________________________________________________________
2.
(1 point) Circle
your Studio instructor/hour:
Lynch /TU 9:30
Matloob /TU 11:30
Regehr /TU 1:30
O’Shea/WF 7:30
Lynch /WF 9:30
Page total:
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9
3.
(6 pts) A car travels on a straight road for 20 km at 40 km/h. It then continues in the
same direction for another 20 km at 60 km/h. What is the average velocity of the car
during the complete trip? (Assume that it moves in the positive
x
direction.)
Δ
t
1
=
Δ
x
1
/v
1
Δ
t
1
=
Δ
x
1
/v
1
= (20 km)/(40 km/h) = 0.5 h
= (20 km)/(60 km/h) = 0.333 h
Since both displacements are in the same direction,
Δ
x
=
Δ
x
1
+
Δ
x
2
= 20 km + 20 km = 40 km.
The total time for the trip is
Δ
t
=
Δ
t
1
+
Δ
t
2
= 0.833 h.
Therefore the average velocity is
v
avg
=
Δ
x/
Δ
t
= (40 km)/(0.833 h) = 48 km/h
Answer________________
4.
The position of an object moving along an
x
axis is given by
x
=
2
t
3
 4
t
+ 5
,
where
x
is in meters and
t
is
in seconds.
a) (5 pts) What is the average velocity between 0 and 3 seconds?
At
t
= 0 s,
x
0
= 0 – 0 + 5 = 5 m
At
t
= 3 s,
x
= 54 – 12
+ 5 = 47 m
v
avg
=
Δ
x/
Δ
t
= (47 – 5 m)/(3 s) = 14 m/s
Answer________________
b) (5 pts) What is the average acceleration between 0 and 3 seconds?
v
(
t
)= d
x
/d
t
= 6
t
2
– 4
At
t
= 0
v
(
t
)= 4 m/s.
(this is initial velocity)
At
t
= 3 s
v
(
t
)= 50 m/s.
(this is final velocity
a
avg
= (
v
–
v
0
)/
Δ
t
= (50

(4) m/s)/ 3 s = 18 m/s
2
Answer________________
c) (5 pts) At what time is the velocity zero?
If there is more than one time, state each of
the times?
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 Spring '08
 oshea
 Physics, Force, Friction, Velocity, partial credit

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