Physics 1021 Chapter Notes - Chapter 1.6: Friction, Electromagnetism

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erinmanatee881

4 Oct 2017

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These forces are called contact forces because one object applies a force on the other because they are in contact with each other. The origin of contact forces relates to electromagnetic forces because charged particles of one object attract and repel charged particles of other objects. The three main forces are: normal force, tension force and spring force, frictional force. When two object are in contact they apply a normal force on each other. The direction of the force is perpendicular to the touching surface. Normal force is denoted as , where n is normal and f is force. When an object is attached to one end of the rope and another end is pulled, a tension force is present. The tension force is denoted , where t is tension and f is force. When two rough surfaces are in contact with each other, frictional force is acting between them.

Related Questions

1. Which of the following describes an object with a non-zero netforce acting on it? Choose all that apply.
The moped accelerated while making a left turn.
The motorcycle traveled at a constant speed while making au-turn.
The truck slowed down while making a right turn.
The spaceship traveled at a constant speed in a straightline.
The car sped up from 50 mph to 65 mph while moving in a straightline.

2. If you observe that an object is accelerating, what should youconclude?
A non-zero net force is acting on it. Only forces causeacceleration. As such, if an object is accelerating it must bebecause a non-zero net force is acting on it.
It must be in free fall.
It must be changing direction. Acceleration is a vector and vectorshave both magnitude and direction. Thus if an object isaccelerating it must be changing direction.
The forces acting on the object must be greater than the forces theobject is exerting.
It must be speeding up. If an object is accelerating that means itis speeding up.

3. Which of the following are true according to Newton's 2nd Law?Choose all that apply.

If the acceleration is zero, then the net force is zero.
If you apply the same force to 2 objects, the one with more masswill have a greater acceleration.
If you apply the same force to 2 objects, the one with less masswill have a greater acceleration.
If two objects have the same acceleration, the one with less masswill have a larger net force exerted on it.
If two objects have the same acceleration, the one with more masswill have a larger net force exerted on it.
The larger the net force on an object is, the larger theacceleration.
The larger the net force on an object is, the smaller theacceleration.

4. A box is on the Moon. The box weighs 152 lb and is in free fall.How much force is the box exerting on the Moon and in whatdirection?

lb
Up
Down
Right
North
East
West
Left
South

5. Which of the following are the correct units for mass? Chooseall that apply.
slugs
u
kgÂ·m/s2
g
N
m/s2
oz
lb

6. If an object is traveling in a circle, which of the followingmust be TRUE? Choose all that apply.
The object is slowing down.
The object is speeding up.
The object has a net force acting on it.
The object has a constant velocity.
The object is accelerating.

1.

While helping a friend move, you push a 11.5 kg dolly with a forceof 11.0 N. Assume there are no other forces acting on the dolly. Ifthe dolly starts at rest, how far does it move in 3.50 s?
1 m

2.

At a lumberjack competition an axe with a mass of 1.25 kg is thrownat a target with a speed of 41 m/s. When it hits the target, itpenetrates to a depth of 0.055 m.
(a) What was the average force exerted by the target on theaxe?
1 N

(b) If the mass of the axe is halved, and the force exerted by thetarget on the axe remains the same, by what multiplicative factordoes the penetration depth change?
2
It doubles. It increases by a factor of the square root of two. Itdoes not change. It decreases by a factor of the square root oftwo. It halves.
Your work in question(s) will also be submitted or saved.
3

Your 1500 kg car pulls a 540 kg trailer away from a stop sign withan acceleration of 2.00 m/s2. (Note the answers should be given inkN.)
(a) What is the net force exerted by the car on the trailer?
1 kN

(b) What force does the trailer exert on the car?
2 kN

(c) What is the net force acting on the car?
3 kN

4.

Two boxes sit next to, and touching, each other on a frictionlesshorizontal surface. The lighter box has a mass of 5.31 kg and theheavier box has a mass of 7.29 kg.
(a) Find the contact force between these boxes when a horizontalforce of 6.1 N is applied to the light one.
1 N

(b) If the 6.1 N force is applied to the heavy box instead, is thecontact force between the boxes the same as, greater than, or lessthan the contact force in part (a)?
2

(c) Verify your answer to part (b) by calculating the contact forcein this case.
3 N

5.

A child sits in a wagon and together they have a mass of 25 kg. Thewagon is pulled with a constant speed by a handle that is at anangle of 22Â° above the horizontal. If the normal force exerted onthe wagon is 210 N, what is the force F applied to thehandle?
1 N

6.

An object acted on by three forces moves with constant velocity.One force acting on the object is in the positive x direction andhas a magnitude of 6.7 N; a second force has a magnitude of 4.5 Nand points in the negative y direction. Find the direction andmagnitude of the third force acting on the object.
1 N
2Â° (counterclockwise from the +x axis)

7.

A chain is used to lift a 1200 kg car vertically upward with anacceleration of 0.90 m/s2. What is the tension in the chain?
1 N

8.

A 22.5 kg box (m1) rests on a table.

(a) What is the weight of the box?
1 N
What is the normal force acting on it?
2 N (upward)
(b) A 12.5 kg box (m2) is placed directly on top of the 22.5 kgbox.
Determine the normal force that the table exerts on the 22.5 kgbox.
3 N (upward)
Determine the normal force that the 22.5 kg box exerts on the 12.5kg box.
4 N (upward)

9.

Your friend has a weight of 127 lb when standing on a scale. Youtake the scale to an elevator where you notice your friend's weighton the scale reads 108 lb. What are the direction and magnitude ofthe elevator's acceleration?
Direction 1
Magnitude 2 m/s2

10.

When you lift a package with a force of 82 N, the packageaccelerates upward at a rate of a. If, instead, you lift with aforce of 93 N, the package now has an acceleration of 8 multipliedby a.
(a) Find the weight of the package.
1 N

(b) Find the acceleration a.
2 m/s2

11.

One 3.1 kg paint bucket is hanging by a massless cord from another3.1 kg paint bucket, also hanging by a massless cord, as shownbelow.

(a) If the buckets are at rest, what is the tension in eachcord?
(lower cord) 1 N
(upper cord) 2 N

(b) If the two buckets are pulled upward with an acceleration of1.30 m/s2 by the upper cord, calculate the tension in eachcord.
(lower cord) 3 N
(upper cord)5

12)
Your friend has a pair of fuzzy dice with a mass of 1.32 g hangingfrom his rear-view mirror.
(a) When he accelerates from a stoplight, the dice deflect backwardtoward the rear of the car hanging at an angle of 6.18Â° relative tothe vertical. Find the tension in the string holding thedice.
N

(b) At what angle to the vertical will the tension in the string betwice the weight of the dice?
Â°

1) An object is moving with constant velocity. Which of thefollowing statements is true?
a) A constant force is being applied in the direction ofmotion.
b) A constant force is being applied in the direction opposite ofmotion.
c) There are no forces acting on the object.
d) The net force on the object is zero.
e) There is no frictional force acting on the object.

2) You apply the same force to two objects. Object 1 has mass M andobject 2 has mass 5M.
a) ten times that of object 1 b) five times that of object 1
c) the same as that of object 1 d) 1/5 as that of object 1

3) An object of weight W is in free-fall close to the surface ofEarth. What is the force that the object exerts on Earth?
a) a force greater than W b) a force less than W
c) a force equal to W d) no force at all

4) A parking crate slides down an inclined ramp at constantvelocity. Thus we can deduce that _
a) a frictional force is acting on it
b) a net downward force is acting on it
c) a net upward force is acting on it
d) it is not acted on by appreciable normal force
e) it is not acted on by appreciable gravitational force

5) A person applies a constant force of 20N to a rock of mass1000kg for a total of 20 seconds. What is the work done by thisperson if the person does not move at all by this appliedforce?
a) 1000J b) 2000J c) 20,000J d) 0J e) 400J

6) If the net work done on an object is positive, then theobject's kinetic energy.
a) decreases b) remains the same c) increases d) is zero

7) You throw a ball straight up. Compare the sign of the workdone by gravity while the ball goes up with the sign of the workdone by gravity while it goes down.
a) Work is + on the way up and + on the way down
b) Work is + on the way up and - on the way down
c) Work is - on the way up and + on the way down
d) Work is - on the way up and - on the way down

Physics 1021 Chapter Notes - Chapter 1.6: Friction, Electromagnetism

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