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Phy 121 Fall 2010 Midterm 1 Solutions:
Form 0
1.
2.
21
10 1
1.5
/
93
xx
v
m s
tt
22
00
2
2
7
1
0.714
/
;
9
2
2
1
3
7 (6
2)
( 0.714) (6
2)
25.3
2
a
m s
x
x
v t
a t
m
3.
3
for very small
: 3t>5 
initial motion is backward;
maximum power of
is 3
is not constant;
ta
4.
There is vacuum on the surface of the moon and all objects fall with the same
speed. Both equations for t and v below do not contain any mass. Thus the mass
doesn’t matter . Since
/
1/ 6
moon
earth
gg
and
2
1
2
2
2
= 6
6
2
/ 6
moon
earth
h
h
h
h
g t
t
t
t
g
g
g
.
With
11
6
6
6
monn
earth
earth
earth
v
g t
v
g
t
v
.
5.
The velocity with which ball 1 arrives at the launch height on its way down is
equal to the launch velocity, but pointing downward. Ball 2 must be thrown
downward with the same velocity. The launch velocity of
ball 1 is:
0
2 (
)
2 (
)
2 9.81 (4.0 1.5)
7.00
/
top
launch
top
launch
v
v
g h
h
v
g h
h
ms
6.
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 Fall '08
 STEPHENS

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