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homework 10 – RAHMAN, TARIQUE – Due: Feb 29 2008, 3:00 am
1
Question 1, chap 7, sect 3.
part 1 of 2
10 points
If a golf ball and a pingpong ball both
move with the same kinetic energy, which has
the greater speed?
1.
Cannot be determined
2.
the golf ball
3.
the pingpong ball
correct
4.
The two balls have the same speed.
Explanation:
Kinetic Energy is
1
2
mv
2
. According to the
assumption
1
2
m
golf
v
2
golf
=
1
2
m
p
−
p
v
2
p
−
p
.
Since
m
golf
> m
p
−
p
, it follows that
v
golf
<
v
p
−
p
.
Question 2, chap 7, sect 3.
part 2 of 2
10 points
In a gaseous mixture of massive molecules
and light molecules with the same average
KE, which have the greater speed?
1.
the light molecules
correct
2.
Cannot be determined
3.
They have the same speed.
4.
the massive molecules
Explanation:
Since
m
massive
> m
light
,v
massive
< v
light
.
Question 3, chap 7, sect 3.
part 1 of 1
10 points
A piece of paper of mass
m
is dropped from
a height
H
, to the ±oor (height = 0). The
force of air friction has magnitude
f
.
The net work
W
net
done on the paper is
1.
W
net
=
mg H .
2.
W
net
=

f H .
3.
W
net
=

mg H .
4.
W
net
=
f H .
5.
W
net
= (
mg

f
)
H .
correct
6.
W
net
= (
f

mg
)
H .
Explanation:
Net work is the work done by net force, so
W
net
=
V
F
net
·
V
D
= (
mg

f
)
H .
Question 4, chap 7, sect 1.
part 1 of 1
10 points
A catcher “gives” with a baseball when
catching it.
If the baseball exerts a force of 473 N on
the glove such that the glove is displaced 5.25
cm, how much work is done by the ball?
Correct answer: 24
.
8325 J (tolerance
±
1 %).
Explanation:
Basic Concept:
W
net
=
F
net
d
cos
θ
=
F
net
d
since
θ
= 0
◦
⇒
cos
θ
= 1.
Given:
F
net
= 473 N
d
= 5
.
25 cm
Solution:
W
net
=
F
net
d
= (473 N)(0
.
0525 m)
= 24
.
8325 J
Question 5, chap 7, sect 3.
part 1 of 3
10 points
A 0
.
419 kg particle has a speed of 8
.
6 m
/
s
at point
A
and kinetic energy of 9
.
8 J at point
B
.
What is its kinetic energy at
A
?
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View Full Documenthomework 10 – RAHMAN, TARIQUE – Due: Feb 29 2008, 3:00 am
2
Correct answer: 15
.
4946 J (tolerance
±
1 %).
Explanation:
Given :
m
= 0
.
419 kg
and
v
A
= 8
.
6 m
/
s
.
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 Fall '08
 Turner
 Physics, Energy, Kinetic Energy, Work

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