Thevalingam, Donald – Homework 8 – Due: Nov 13 2006, midnight – Inst: Eslami
1
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17
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001
(part 1 of 1) 10 points
For the ballistic missile aimed to achieve the
maximum range of 17500 km, what is the
maximum altitude reached in the trajectory?
Correct answer: 4375 km.
Explanation:
For the maximum range
R
, the launch angle
is 45
◦
and the range
R
is
R
=
v
2
0
sin(2
θ
)
g
=
v
2
0
sin[2 (45
◦
)]
g
=
v
2
0
g
.
The height
H
is given by
H
=
v
2
0
sin
2
(
θ
)
2
g
=
v
2
0
4
g
.
So dividing
H
by
R
gives
H
=
1
4
R
=
1
4
(17500 km)
=
4375 km
.
keywords:
002
(part 1 of 3) 10 points
An object has a mass of 39 kg.
The acceleration of gravity is 9
.
8 m
/
s
2
.
What is its weight on the earth?
Correct answer: 382
.
2 N.
Explanation:
g
= 9
.
8 m
/
s
2
and
W
=
m g
= 39 kg 9
.
8 m
/
s
2
= 382
.
2 N
003
(part 2 of 3) 10 points
What is its mass on the moon where the force
of gravity is
1
6
that of the earth?
Correct answer: 39 kg.
Explanation:
The mass stays the same.
004
(part 3 of 3) 10 points
What is the weight of that object on the
moon?
Correct answer: 63
.
7 N.
Explanation:
g
m
=
1
6
g
e
, so
W
m
=
m g
m
=
m
g
e
6
= (39 kg)
9
.
8 m
/
s
2
6
= 63
.
7 N
keywords:
005
(part 1 of 1) 10 points
A ball of mass
M
is suspended by a thin
string (of negligible mass). An upward force
F
pulls on the string as shown in the figure
below.
The relation between the tension in
the string
T
and the weight of the ball
M g
is
given in each statement below.
M
T
F
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Thevalingam, Donald – Homework 8 – Due: Nov 13 2006, midnight – Inst: Eslami
2
While
T
< M g ,
the ball’s acceleration
must be constant, with its velocity either up
wards, downwards, or zero.
1.
True
2.
Cannot be determined.
3.
False
correct
Explanation:
In the vertical direction
T

M g
=
m a .
Since
a
= 0
,
we have
T
=
M g .
The direction
of the velocity doesn’t matter.
keywords:
006
(part 1 of 1) 10 points
A man stands in an elevator in the university’s
administration building and is accelerating
upwards.
(During peak hours, this does not
happen very often.)
Elevator
Cable
Choose the correct free body diagram for
the man, where
F
i,j
is the force on the object
i
, from the object
j
.
1.
F
F
elevator, cable
man, earth
2.
F
man, floor
F
elevator, cable
F
man, earth
3.
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 Spring '08
 Turner
 Physics, Force, Mass, Work, Correct Answer, kg, Thevalingam

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