Gozick, Brandon – Homework 8 – Due: Oct 6 2006, 5:00 pm – Inst: D Weathers
1
This
printout
should
have
11
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
The due time is Central
time.
001
(part 1 of 1) 10 points
A cheerleader lifts his 24 kg partner straight
up off the ground a distance of 0
.
268 m before
releasing her.
The acceleration of gravity is 9
.
8 m
/
s
2
.
If he does this 11 times, how much work has
he done?
Correct answer: 693
.
37 J.
Explanation:
The work done in lifting the cheerleader
once is
W
1
=
m g h
= (24 kg)(9
.
8 m
/
s
2
)(0
.
268 m)
= 63
.
0336 J
.
The work required to lift her
n
= 11 times is
W
=
n W
1
= (11)(63
.
0336 J) = 693
.
37 J
.
keywords:
002
(part 1 of 1) 10 points
A man cleaning his apartment pushes a vac
uum cleaner with a force of magnitude 24
.
6 N.
The force makes an angle of 16
.
2
◦
with the hor
izontal floor.
The vacuum cleaner is pushed
2
.
01 m to the right along the floor.
Calculate the work done by the 24
.
6 N
force.
Correct answer: 47
.
4827 J.
Explanation:
Using the definition of work, we have
W
=
~
F
·
~s
=
F s
cos
θ
= (24
.
6 N) (2
.
01 m) cos 16
.
2
◦
= 47
.
4827 J
.
Note:
The normal force
N
, the weight
m~g
,
and the upward component of the applied
force, (24
.
6 N) sin 16
.
2
◦
, does no work because
they are perpendicular to the displacement.
keywords:
003
(part 1 of 3) 0 points
A cart loaded with bricks has a total mass
of 9
.
3 kg and is pulled at constant speed by
a rope.
The rope is inclined at 21
.
2
◦
above
the horizontal and the cart moves 30
.
9 m on
a horizontal floor.
The coefficient of kinetic
friction between ground and cart is 0
.
6
.
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 Fall '08
 Weathers
 mechanics, Energy, Force, Work, Correct Answer, Gozick

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