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DA T E - . P E R I O D -
:
C HAPTER :
F'
NAM E
C H A P TE R :
F:
): Evaluation
): E valuation
B. Applying
Concepts
Answer the following questions in two or three complete senlences.
FORCES
1. E xpl ai ntherel ati onshi pbetweenmas s andw ei ghtonE arth.W oul dthi s rel ati ons hi pc hangeonMars ?
E xol ai nvour answ er.
A. Testing
Concepts
The weight of any object is proportionalto the mass of the obJect.The force of gravity on Mars would
be differentfrom the force of gravity on Earth. Mass would not change, but weight would change.
However,mass and weight would still be proportional.
ln the space to the left, write the letter of the answer to each question
1. b
The attractiveforce that acts between all objects rs
a. electromagneticforce
b. gravitationalforce
c. strong nuclear force
d. weak nuclear force
c
b. gravitationalforce
d. weak nuclear force.
The station wagon is more ditficult to stop because it has a greater mass.
Metals such as copper can be pounded into thin sheetsdue to
a. electromagneticforce
b. gravitationalforce
c. strong nuclear force
d. weak nuclear force.
4. a
According to NeMon's law, an object with no net force acting on it remains at
r e s to r i n m o tio n with a co n sta n tve lo city.
a. first
b . se co n d c. th ir d
5. o
law statesthat the accelerationof a body is directly proportional to the
NeMon's net force on it and inverselyproportionalto its mass.
a. first
b . se co n d c. th ir d
6. D
L o s i n gs p e e da s yo u r id e yo u r b ike u p h ill d e m o n s trates
N eMon's _
a. first
b . se co n d c. th ir d
7. a
Two teamsin a tug of war exert the sameamount of force on each other and the rope does
not move. NeMon's law explainswhy the rope does not move.
a . f i r s t b . se co n d c. th ir d
8. c
lf you push againsta wall, the wall pushes back againstyou with _
o . te ss c. e q u a t
a. no
d. more
9. a
The gravitationalforce exefted by a large body, such as Earth,is
a. weight
b. mass c. acceleration d. inertial mass.
3. A n el evatori s travel i ngfrom t he l obby to the top of the bui l di ng.A s i t s topson the top fl oor, i n
w hi ch di recti oni s i ts accel er ati on?
E x ol ai n.
force.
Mass and weight are related by
a. the force of gravity
b. newtons
11 . c
D i f f i c u l t yi n p u sh in ga la r g ecr a te fr o m r e st in vo lves
a. gravity
b. sliding friction
c. static friction
d. balancedforces.
12. c
When the drag force on an object equals the force of gravity,_
occurs.
a . a c c e l e r atio n b . in e r tia lm a ss c. te r m in a lvel oci ty d. maxi mum mass
13. o
The effectof air resistanceon the tail of a kite is body of the kite.
b . le ssth a n
a . t h e s a m ea s
c. m o r e th a n
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--l
14. a
c. friction
When an object slows down, its acceleralionis in the direction opposite to the velocity of the obiect.
The accelerationof the elevatoris down.
4. In the drawing at right, use arrows to
show the two horizontaland two vertical forces acting on the boat as it is
pulled to the shore.Isthere a net force
on the boat?
l aw .
10. a
C
--l
2. Why is it easierto stop a compact car than a large station wagon when both are moving at the
same speed?
3. a
m
-z
The strongestforce is
a. electromagneticforce
c. strong nuclear force
d. none of these.
Yes, there is a net force on the boat in
the directionof the personpullingit
from the waler.
Explainthe differencebetweenactionreactionforcesand net forces.Usingthe
boat show n i n the fi gure,desc ri bean
exampl eof each.
Action-reactionforces act on differentobjects, and are equal in magnitude but opposite in direction.
Several examplesmay be found. The girl pulling the boat demonstratesaction-reactionpairs in that
she pulls againstthe boat with the same force that the boat pulls againsther. The forces,though,are
in oppositedirections.Net forces act on the same ob.iectand are not necessarilyequal in magnitude.
The pull of the girl on the boat is greaterthan the opposingpull of friction,so the boat moves in the
directionol the girl.
6. What is the relationshipbetweenslidingfriction and speed?Betweenslidingfrictionand normal force?
Slidingtrictionis independentof speed.Slidingfrictionis proportionalto normalforce.
the effect of air resistanceon the
7. S upposeyou try to pul l a rope ti ed to a l argec arton. Y ou c annot mov e the c arton. W hat forc es
are acti ngon your hand?
lf the force of gravityon a balloon is 3000 N, and the lift force provided by the atmosphere
is 3300 N, in which direction is the net force acting?
b. downward
a. upward
c. toward the east
d. There is no net force.
EVALU AT ION I5
The forces acting on your hand are the forces exerted by your arm muscles and the force exerted by
the rope.
16 E V A LU A TION
C HAPTER
5
NAME
m
C
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C. Understanding
Concepts
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1. What force is required to acceleratea 6.Gkg bowling ball at +2.0 mls2?
D. Extending
Concepts
1. An elevator has a massof 1.10 x lO3 kg. Supposeit acceleratesupward at 0.45 mls2.What is the
force acting on the elevator'ssupport cable?
F=ma
= (6.0 kgx+2.0 m/sz)
= +12N
W=mg
= (1.10 x ld kgx-9.80 m/s2)
= -1.08 x 10r N
2. What is the mass of a cat that weighs 30.0 N?
w=m s
Fret=F"*F*
= (+4.95 x i d N ) + (+1.08 x 10 N )
=1.12x1dN
= 3.06 kg
Accelerationdue to gravity on Mars is 3.8 m/s2.
a. Would a 5.0-kg watermelon weigh more on Earth or on Mars?
2. A rocket weighs 2.0 x 107 N. lts engines exert +25 x 106 N of force at lift-off.
We = nEe
Wu = m9u
= (5.0 kgXg.BOnVsr)
= (5.0 ksx3.8om/*)
= 49N
= 19N
It would weigh more on Earth
a. What is the mass of the rocket?
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b. How would the mass of the watermelon differ?
b. What is its acceleration when it lifts off?
4. What is the inertial mass of a 75-N dog?
Fa=Fa+W
= (+25 x 1S N ) + (-2.0 x 107N )
=+5.0xl S N
-F m a m = a
r=
m = (15 N/(9.8 m/sr)
= 7.2 kg
How much force is neededto keep a 78-kg box moving at a constantvelocity acrossa warehouse
floor if the coefficientof friction between the box and the floor is 0.21?
a= FM
m
= (+ 5.0 x l ff N )
(2.0 x 100N)
= 2.5 m/s2
c. Theaverageaccel erati ono ftheroc k etduri ngi ts T.0mi nutel aunc hi s l 0.0m/s 2.W hatv el oc i tv
does it reach?
v=at
= (10.0 m/s2x7.0minxoo s/min)
= 4Z)0 m/s
f i= pFN
= (0.21X760
N)
= 160N
6. A 597-N cross-countryskier is moving over packed snow. The coefficientof friction between the
skis and the snow is 0.11. What force is required to keep the skier moving at a constant speed?
A 47-N box is pulled along a horizontalsurfaceby a 25-N weight hangingfrom a cord along a frictionlesspulley.
Fe = tfin
= (0-11x5s7N)
= 66N
a. What is the accelerationof the box and the weight?
n . =W
tl
= (47 Ny(9.8nr/sr)
= 4.8 kg
What is the coefficient of friction between a 65-kg roller skater and the floor of the roller rink if the
skater moves at a constant speed with a force of 75 N?
Fm 4 = W = m g
= (65 kgxg.B m/s2)
= 6a0N
E
=
,1
=W
.tott'l)
- (i.o ,,
(9.8 m/s2)
= 2.0 x .106kg
Mass would remain the same.
= [/B kgxe.Bm/s3)
=76 0N
Fa= aa
= (1.10 x 1d kg[+0.45 m/sz)
= 4.95 x l GN
Net force is the sum of the force that causes acceleralion(+4.95 x iG N) and th€ upward force that
balancesthe weight of the elevator (+1.08 x 10a N)
^=YY
(30.0
N)
"' - (9.a0mE4
F 1 1=W=6 9
NAME
5 Evaluation
,Evaluation
--
-z
C H A P TE R
m r =i w
= (25 Ny(g.Sm/sr)
= 2.6 kg
b. What force is exertedon the cord?
F*a = ma
= (4.8 kgx3.4nr/sr)
= 16N
FN=
= c/5N)
(640 N)
= O.'12
EVALUATION 17
I8
EVALUATION
F
a=
lfl6
*
lll,
25N
(4.8 kg) + (2.6 kg)
= 3.4 m/*
=