lim (kl9356) – Homework 6 – Weathers – (17104)
1
This
printout
should
have
10
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0 points
Joe pushes down the length of the handle
of a(n) 12
.
2 kg lawn spreader.
The handle
makes an angle of 42
.
1
◦
with the horizontal.
Joe wishes to accelerate the spreader from
rest to 1
.
32 m
/
s in 1
.
3 s.
What force must Joe apply to the handle?
Correct answer: 16
.
6956 N.
Explanation:
The horizontal component of the force is
F
h
=
F
cos
θ.
Let
v
be the final velocity of the spreader.
According to Newton’s second law,
F
h
=
m a
h
so
F
cos
θ
=
m
Δ
v
h
Δ
t
F
=
m
Δ
v
h
Δ
t
cos
θ
=
m v
t
cos
θ
=
(12
.
2 kg) (1
.
32 m
/
s)
(1
.
3 s) cos 42
.
1
◦
= 16
.
6956 N
002
10.0 points
A 55 kg boy and a 37 kg girl use an elastic rope
while engaged in a tugofwar on a frictionless
icy surface.
If the acceleration of the girl toward the
boy is 2
.
8 m
/
s
2
, determine the magnitude of
the acceleration of the boy toward the girl.
Correct answer: 1
.
88364 m
/
s
2
.
Explanation:
According to Newton’s Third Law of Mo
tion the force the boy exerts on the girl is the
same as the force the girl exerts on the boy, so
F
g
=
F
b
m
g
a
g
=
m
b
a
b
a
b
=
m
g
a
g
m
b
003
(part 1 of 2) 10.0 points
An object in equilibrium has three forces ex
erted on it. A(n) 38 N force acts at 73
.
6
◦
, and
a(n) 49 N force acts at 38
.
9
◦
.
What is the direction of the third force?
(Consider all angles to be measured counter
clockwise from the positive
x
axis.)
Correct answer: 233
.
988
◦
.
Explanation:
Basic Concepts:
Choose a coordinate system with the pos
itive
x
axis representing 0
◦
and the positive
yaxis representing 90
◦
.
Any force
F
has an
x
component of
F
x
=
F
cos
θ
and a
y
component of
F
y
=
F
sin
θ
where
θ
is measured from the
x
axis.
Solution:
Since
F
1
and
F
2
act up and to the right, the
force
F
must act down and to the left, so
F
lies in the third quadrant.
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 Fall '08
 Weathers
 Magnetism, Acceleration, Force, Friction, Mass, Work, lim, kg

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