Version 099/ABCAD – QTest #7 – Antoniewicz – (56445)
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001 (part 1 of 2) 5.0 points
You throw a ball of mass 1
.
5 kg straight up.
You observe that it takes 2
.
1 s to go up and
down, returning to your hand.
assuming we
can neglect air resistance, the time it takes
to go up to the top is half the total time,
1
.
05 s. Note that at the top, the momentum is
momentarily zero, as it changes from heading
upward to heading downward.
Use the Momentum Principle to determine
the speed that the ball had just after it left
your hand. Use
g
= 9
.
8 m
/
s
2
.
1. 14.21
2. 15.68
3. 16.66
4. 10.29
5. 12.74
6. 13.23
7. 11.76
8. 10.78
9. 13.72
10. 16.17
Correct answer: 10
.
29 m
/
s.
Explanation:
We can write
F
net
=
Δ
p
Δ
t

m g
=
m
(
v
f,y

v
i,y
)
Δ
t

m g
=
0

m v
i,y
Δ
t
⇒
v
i,y
=
g
Δ
t
=
(
9
.
8 m
/
s
2
)
(1
.
05 s)
=
10
.
29 m
/
s
.
002 (part 2 of 2) 5.0 points
Use the Energy Principle to determine the
maximum height above your hand reached by
the ball.
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 Fall '08
 Turner
 Mass, Correct Answer

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