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5 E, valuation
FORCES
A. TestingConcepts
ln the space to the left, write the letter of the answer to each question.
1. -
The attractiveforce that acts between all objects is
a. electromagneticforce
b. gravitationalforce
c. strongnuclearforce
d. weak nuclearforce.
2. -
The strongestforce is
a. electromagneticforce
c. strongnuclearforce
b. gravitationalforce
d. weak nuclearforce.
3. -
Metalssuch as copper can be pounded into thin sheetsdue to
a. electromagneticforce
b. gravitationalforce
c. strongnuclearforce
d. weak nuclearforce.
4. -
According to NeMon's law, an object with no net force acting on it remains at
rest or in motion with a constantvelocity.
a. first
b. second
c. third
5. -
NeMon's law statesthat the accelerationof a body is directly proportional to the
net force on it and inverselyproportionalto its mass.
a. first
b. second
c. third
6. -
Losingspeedas you ride your bike uphill demonstrates
Newton'sa. first
b. second
c. third
7. -
Two teams in a tug of war exeft the sameamount of force on each other and the rope does
not move. Newton's_
law explainswhy the rope does not move.
a. first
b. second
c. third
B. -
lf you push againsta wall, the wall pushesback againstyou with a. no
b. less c. equal
d. more
9. -
The gravitationalforce exerted by a large body, such as Earth,is
a. weight
b. mass c. acceleration d. inertialmass.
10. -
Mass and weight are related by
a. the force of gravity
b. newtons
c. friction
law.
force.
d. none of these.
1'1.-
Difficulty in pushing a large crate from rest involves
a. gravity
b. sliding friction
c. staticfriction
d. balancedforces.
12. -
When the drag force on an object equals the force of graviry,occurs.
a. acceleration b. inertialmass c. terminalvelocitv
d. maximum mass
13. -
The effect of air resistanceon the tail of a kite is body of the kite.
a. the same as
b. lessthan
c. more than
14. -
lf the force of gravityon a balloon is 3000 N, and the lift force provided by the atmosphere
is 3300 N, in which directionis the net force acting?
a. upward
b. downward
c. toward the east
d. There is no net force.
the effect of air resistanceon the
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5 Evaluation
B. ApplyingConcepts
Answer the following questions in two or three complete sentences.
1. Explainthe relationshipbetweenmassand weight on Earth.Would this relationshipchangeon Mars?
Explainyour answer.
2. Why is it easierto stopa compactcar than a largestationwagonwhen both are movingat the
samespeed?
3. An elevatoris travelingfrom the lobbyto the top of the building.As it stopson the top floor, in
which directionis its acceleration?
Exolain.
4. In the drawingat right,usearrowsto
showthe two horizontaland two vertical forcesactingon the boat as it is
pulledto the shore.lstherea netforce
on the boat?
5. Explainthe difference
betweenactionreactionforcesand netforces.Usingthe
boat shownin the figure,describean
exampleof each.
6. Whatisthe relationship
betweenslidingfrictionandspeed?
Between
slidingfrictionand normalforce?
7. Supposeyou try to pull a rope tied to a largecarton.You cannotmove the carton.What forces
are actingon your hand?
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C. Understanding
Concepts
1. What force is requiredto accelerate
a 6.0-kgbowlingball at +2.0 mls2?
2. What is the massof a cat that weighs30.0 N?
3. Accelerationdue to gravity on Mars is 3.8 m/s2.
a. Would a 5.0-kg watermelon weigh more on Earth or on Mars?
b. How would the massof the watermelondiffer?
4. What is the inertialmassof a 75-Ndog?
5. How much forceis neededto keepa 7}-kgbox movingat a constantvelocityacrossa warehouse
floor if the coefficientof frictionbetweenthe box and the floor is 0.21?
6. A 597-Ncross-country
skieris movingover packedsnow.The coefficientof frictionbetweenthe
skisand the snow is 0.11.What force is requiredto keepthe skiermovingat a constantspeed?
7. What is the coefficient
of frictionbetweena 65-kgrollerskaterand the floor of the rollerrink if the
skatermovesat a constantspeedwith a force of z5 N?
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D. ExtendingConcepts
1. An elevatorhasa massof 1.10 x 103kg. Supposeit accelerates
upwardat 0.45 m/s2.What is the
force actingon the elevator'ssupportcable?
2. A rocketweighs2.O x 10i N. lts enginesexert +25 x 106N of force at lift-off.
a. What is the massof the rocket?
b. What is its accelerationwhen it liftsoff?
c. The averageacceleration
of the rocketduringits 7.0 minutelaunchis 10.0m/s2.What velocity
does it reach?
3. A 47-N box is pulledalonga horizontalsurfaceby a 25-Nweighthangingfrom a cord alonga frictionlesspulley.
a. What is the acceleration
of the box and the weight?
b. What force is exertedon the cord?
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