Download Key - Friction Packet

____
Name:
Friction and Newton’s Second Law
*Use the following three relationships to solve the problems below:
a=1!
Fgrav
=
m*g
Use Acceleration due to gravity, g
=
Ffrict
IJ
=
*
Fnorm
10 m/sN
1) An applied force of 50 N is used to accelerate an object to the right across a frictional
surface. The object encounters 10 N of friction. Use the diagram to determine the
normal force, the net force, the mass, and the acceleration of the object. (Neglect air
resistance.)
+
çoi
norm
Ffrictl 0
app
Fqray
iOv’,4t
=
50 N
80 N
m=___
/
5a4,/’L
6
-
F-
a4i\i
fry’
F net =40t%
2) An applied force of 20 N is used to accelerate an object to the right across a frictional
surface. The object encounters 10 N of friction. Use the diagram to determine the
normal force, the net force, the coefficient of friction (p) between the object and the
surface, the mass, and the acceleration of the object. (Neglect air resistance.)
(
Fnorm=
FfrictlO N
!app =20 N
M
N
j1=
m=
net
.
io
‘I’
-
cc€\.y)
___
________
3) A 5-kg object is sliding to the right and encountering a friction force that slows it
down. The coefficient of friction (p) between the object and the surface is 0.1.
Determine the force of gravity, the normal force, the force of friction, the net force,
and the acceleration. (Neglect air resistance.)
(
:
A
.
J
Ffrict..j
2*’
-
5W
1
=
I
Fgrav
0i’
m
=
oN
1 no y
Fnorm=W
cotJ
5 kg
kL*”
1
F net =5tJ
a
=
rç
)
—
—I
I
I2
6
‘i
4. Edwardo applies a 4.25-N rightward force to a 0.765-kg book to accelerate it across a
tabletop. The coefficient of friction between the book,,9cj the tabletop is 0.4 10. Determine
the acceleration of the book.
iv4
c1; 2 c n
k:
4
F
%)
1itJ
CA:*E:
I
.
(
5. In a physics lab, Kate and Rob use a hanging mass and pulley system to exert a 2.45 N
rightward force on a 0.500-kg cart to accelerate it across a low-friction track. If the total
resistance force to the motion of the cart is 0.72 N, then what is the cart’s acceleration?
4Sr1
1
(
fr’
2
/s
N
A
_________.
Name:
Forces in Two Dimensions
<6y
Inclined Plane Analysis
Read from Lesson 3 of the Vectors and Motion in Two-Dimensions chapter at The Physics Classroom:
http://www.physicsc1assroom.com/C1ass/vectors/u313e.htiu1
MOP Connection:
Forces in Two Dimensions: sublevels 5 and 6
Review:
A normal force is a force that is always directe4
1.
c. perpendicular to the surface the object is touching
b. sideways
a. upwards
2.
An object is upon a surface. The normal force is equal to the force of gravity
b. only when the object is at rest
a. in all situations
d. only when there is no vertical acceleration
accelerating
c only when the..objçct
thereis no vertical accelerabon AND 1
iorm and Fgrav are the only vertical forces
..
Getting the Forces Right:
3. The object at the right has been placed on a tilted surface or inclined
plane. If there is enough tilt, it will accelerate from rest and begin its
motion down the incline. Draw a free-body diagram for the object
? sliding down the rough incline. Label the three forces according to
type (Fgrav
Ffricb Fair, Ftens, Fapp etc.).
Physics Tip: When you encounter a situation involving a force directed at angles to all other forces,
immediately convert the uncooperative force(s) into two perpendicular components. Use SOH CAH TOA
to resolve any uncooperative force into components directed at right angles to each other. One
component should be in the direction of the acceleration; the other should be perpendicular to it. In the
case of inclined planes, resolve the uncooperative force into components parallel and perpendicular to the
inclined plane.
The force of gravity (or weight vector) is the uncooperativeforce. It is
4.
typically resolved into two components one parallel to the plane
and the other perpendicular to the plane. Given the diagram at the
right with the two components of gravity represented as i and Fj.,
use trigonometric functions to write equations relating these
components to the force of gravity.
-
FU=())
5.
fr’()
II.=
(
()
1F1
For the three situations described below, use <, >, or = symbols to complete the statements.
Object accelerates down
Object moves at constant speed.
Object at rest.
incline.
Fim
Ffrict
Ffnct
Fti
:
,
1
F
F
=
1A
ru
Ffrjd
Fnorm
=
-__
“
© The Physics Classroom, 2009
Ffrjd
11
F
1
F
>
=
Ffrjd
Fnorm
)>
Page 1
___
________N
_____N
_____N
Forces in Two Dimensions
Use equations for calculating the components of gravity (#4) and Newton’s laws to fill in the blanks.
6. A 4.50-kg object cceler rig down an inclined plane indined at 36.0° (with the horizontal) and
having a coefficient of friction of 0.548.
NVI,FIXiCt
S
NF
!9,%EN
()
(9’15,v
cç (ZJP
:
4.5Zk /€/
•
;1)
(3k )
1F1( k4#1,)
:S()
i4
a
7.
A 65.0-kg crate remains at rest on an inclined plane that is indined at 23.0° (with the horizontal).
9
Pi.
“mFils
,1iSEN
L,,
W
0
—
= 2jj
1
r
N
-
O.4Z.
=
5
Fj=
N
(0
1
S
4
0
=
ic
8.
tl
i(z3)2s4p4
= 2S4(LN
1
r,
=____
N
Acc
a
=_____
rv’
A 41.3-kg box slides down an inclined plane (inclined at 29.1 d’egrees) at a constant speed of 2.1 m/s.
C6 (29, i)
:(4i3 .ic/,)
3(
c
0
J
(6$($I)
IL
FJ3CcJ
N
ZOIN
=____
4
3Co0
=
N
frict
T
pMsCji(2’.1)
j=Q
m
’
4
3icg
(41.3w
N
./i)e (i.)
Zoi,i
net=
W)
0
N
Ac
1
h
’.
a
QmFils
The Tilted Head Trick
Inclined plane problems can be easy. Resolve gravity into its components. Then, ignore the force of
gravity. Finally, tilt the paper or your head and the problem becomes a simple Fnet= m•a problem.
Fd
FMa
\
Pr
\
/
1
F
/
Fftjdr
/
I
r
it
1 \?
(s\’Je()
© The Physics Classroom, 2009
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cpfleVS
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