#### Transcript Main Idea 4 - Forces

```AP Physics - Mechanics
Concept Review and Practice Multiple Choice
Semester 1 Exam
Here’s how this works...
This is an overview of the MAIN topics that we covered first semester.
This is in no way a complete list of everything that was covered. Do not
rely on this as your only source of preparation for the semester exam.
To best prepare be sure to utilize all of your resources (which include
class notes, old tests/quizzes, practice free response questions, and
textbooks).
Main Idea 1 - Kinematics
- Distance v Displacement
- Speed v Velocity
- average and instantaneous
- Acceleration
- average and instantaneous
- Graphing
You need to be
comfortable
with both
algebraic and
calculus-based
expressions.
Main Idea 1 - Kinematics
1) A particle moves from x0 = 30 cm to x = –40 cm in 5 s. The average
velocity of the particle during this time interval is
A) 2 cm/s
B) –2 cm/s
C) 14 cm/s
D) –14 cm/s
E) –140 cm/s
Main Idea 1 - Kinematics
2) You drive for 30 min at 100 km/h and then stop for 15 min. You then drive
for 45 min at 80 km/h. Your average speed for the entire trip is
A) 73 km/h
B) 83 km/h
C) 88 km/h
D) 90 km/h
E) 97 km/h
Main Idea 1 - Kinematics
3) The displacement of an object for a round trip between two locations
A)is always greater than zero.
B)is always less than zero.
C)is zero.
D)can be greater than or less than but not equal to zero.
E) can have any value.
4) The displacement of an object during any time interval is always ________
the distance it travels during that same time interval.
A) greater than or equal to
D) greater than
B) less than or equal to
E) much greater than
C) equal to
Main Idea 1 - Kinematics
5) An object, located at
the origin when t = 0,
moves along the x axis
as shown in the
diagram. At which
point is the object
farthest from its starting point?
Main Idea 1 - Kinematics
6) Which of the curves best describes a body
moving with a constant non-zero acceleration?
Main Idea 1 - Kinematics
7) Which graph of v versus t best describes the motion of a particle whose
velocity is constant and negative?
8) In which graph of v versus t does the particle end up closest to its starting
point?
9) In which graph of v versus t does the particle end up farthest from its
starting point?
Main Idea 1 - Kinematics
10)The relationship between the velocity of a body moving along the x axis
and time is given by
v = 3t2 – 2t, where the units are SI units. The total distance the body
travels between the times t = 2 s and t = 4 s is
A) 12 m B) 60 m C) 48 m D) 34 m E) 44 m
Main Idea 1 - Kinematics
11)The graph shows the instantaneous velocity of a car during 15 s of its
motion. The distance traveled by this car during this 15-s interval is:
A) 30 m B) 450 m C) 300 m D) 75 m E) 375 m
Main Idea 1 - Kinematics
The motion of an object is given by v(t) = 2t3+2t, where v is in m/s and time is in
seconds. At t = 0 the object is at rest at the the origin.
12) The expression for the acceleration a(t) is:
a) 6t2 + 2
b) 6t2 + 2
e) none of these
c) ⅔t3 + t
d) ½t4+ t2
13) The expression for the position x(t) is:
a) 6t2 + 2
b) 6t2 + 2
e) none of these
c) ⅔t3 + t
d) ½t4+ t2
14) The average velocity of the object between 2 and 5 seconds is:
a) 120
b)140
c) 109 d) 169 e) none of these
Main Idea 1 - Kinematics
Answers for questions in this section:
1) D
2) A
3) C
4) B
5) B
6) D
7) B
8) D
9) A
10) E
11) E
12) A
13) D
14) C
Main Idea 1 - Kinematics
Answers for questions in this section:
1) D
2) A
3) C
4) B
5) B
6) D
7) B
8) D
9) A
10) E
11) E
12) A
13) D
average velocity is the
14) C
displacement over time - it is x(5)x(2)
5-2
Main Idea 1 - Kinematics
If this is an area that gives you trouble use the following for additional support/practice.
http://www.slideshare.net/Mrreynon/ap-physics-chapter-2-powerpoint-1869624
Use the youtube channel “Lasseviren” for help
on specific topics/applications. You can search
the channel for specific topics. Not super fancy,
but great physics!
Main Idea 2 - Uniform Acceleration
and Free Fall
- Kinematics Equations for uniform
acceleration (aka...Big 5)
- Law of Falling Bodies
Main Idea 2 - Uniform Acceleration
and Free Fall
1) A particle decelerates uniformly from a speed of 30 cm/s to rest in a time
interval of 5.0 s. It then has a uniform acceleration of 10 cm/s2 for another
5.0 s. The particle moves in the same direction along a straight line. The
average speed over the whole time interval is
A) 20 cm/s
B) 35 cm/s
C) 38 cm/s
D) 100 cm/s
E) 12 cm/s
Main Idea 2 - Uniform Acceleration
and Free Fall
2) For uniformly accelerated motion, which of the following quantities must be
zero?
A. the initial velocity
D) the rate of change of the
velocity
B. the initial displacement
E) the rate of change of the displacement
C. the rate of change of the acceleration
Main Idea 2 - Uniform Acceleration
and Free Fall
3) A car is travelling at 120 km/h (75 mph). When applied the braking system
can stop the car with a deceleration rate of 9.0 m/s2. The typical reaction
time for an alert driver is 0.5 s versus 2 s for a sleepy driver. Assuming a
typical car length of 5 m, calculate the number of additional car lengths it
takes the sleepy driver to stop compared to the alert driver.
A) 13
B) 3.0
C) 10
D) 16
E) 26
Main Idea 2 - Uniform Acceleration
and Free Fall
4) An object is dropped from rest near the surface of the earth. If the time
interval during which it falls is cut in half, the distance it falls will
A) double.
B) decrease by one-half.
C) increase by a factor of four.
D) decrease by a factor of four.
E) not change.
Main Idea 2 - Uniform Acceleration
and Free Fall
5) An object falling near the surface of the earth has a constant acceleration
of 9.8 m/s2. This means that the:
A) object falls 9.8 m during the first second of its motion.
B) object falls 9.8 m during each second of its motion.
C) speed of the object increases by 9.8 m/s during each second of its motion.
D)acceleration of the object increases by 9.8 m/s2 during each second of its
motion.
E)force of gravity on the object must be 9.8 N.
Main Idea 2 - Uniform Acceleration
and Free Fall
6) A ball has been thrown vertically upward. The graph shows the ball's position as a
function of time. Which one of the following statements best describes the motion of
the ball?
A)The velocity of the ball is the same at points A, B, C, D, and E.
B)The acceleration of the ball is 9.8 m/s2 at points A, B, D, and E and zero at point C.
C)The acceleration of the ball is –9.8 m/s2 at points A, B, D, and E and zero at point C.
D)The ball is the same distance above the ground at
points B and D.
E)The velocity of the ball changes continuously
during its flight.
Main Idea 2 - Uniform Acceleration and Free Fall
Answers for questions in this section:
1) A
2) C
3) C
4) D
5) C
6) E
Main Idea 2 - Uniform Acceleration and Free Fall
Answers for questions in this section:
1) A
2) C
3) C
4) D
5) C
6) E
Although I did not include a lot of practice questions for this section it IS a big deal (I just think you don’t need
much practice). Remember…
The acceleration of an object (neglecting air resistance) is always 9.8m/s2 DOWN. How you choose to
mathematically deal with the DOWN part is up to you. It is usually most efficient to use vectors and call all
quantities that act up (or are above the point of release) as positive and all quantities that act down (or are
below the point of release) as negative. In this method you have to consider the sign of all of the quantities
that you are working with (d, v and a). You can also look at the acceleration as an increase in speed (so a =
9.8m/s2 when the object is gaining speed) or a decrease in speed (so a = - 9.8m/s2 when the object is losing
speed). For this method only the sign of the acceleration needs to be considered - all other quantities you
consider the magnitude (positive value) only.
Main Idea 2 - Uniform Acceleration
and Free Fall
If this is an area that gives you trouble use the following for additional support/practice.
http://www.slideshare.net/Mrreynon/ap-physics-chapter-3powerpoint?qid=9a71a571-6c16-460a-8a9f1a2d42088547&v=qf1&b=&from_search=1
Use the youtube channel “Lasseviren” for help
on specific topics/applications. You can search
the channel for specific topics. Not super fancy,
but great physics!
Main Idea 3 - Vectors and 2D Motion
- Vectors v Scalars
- Vector Mathematics
- unit vectors
-
scalar multiplication
vector multiplication (scalar product (dot))
vector multiplication (vector product (cross))
- Relative Motion
- Projectile Motion
Main Idea 3 - Vectors and 2D Motion
1) Assume that the Deschutes River has straight and parallel banks and that
the current is 0.75 m/s. Drifting down the river, you fall out of your boat
and immediately grab a piling of the Warm Springs Bridge. You hold on for
40 s and then swim after the boat with a speed relative to the water of 0.95
m/s. The distance of the boat downstream from the bridge when you catch
it is
A) 67 m
B) 90 m
C) 78 m
D) 54 m
E) 120 m
Main Idea 3 - Vectors and 2D Motion
2) A Ford truck enters a highway and travels at a uniform speed of 50 mph.
Half an hour later a Jaguar enters the highway at the same junction and
heads in the same direction at 55 mph. How long after the Ford entered
the highway does the Jaguar catch up with the truck?
A) 5.0 hrs
B) 6.0 hrs
C) 1.0 hrs
D) 1.6 hrs
E) 5.5 hrs
Main Idea 3 - Vectors and 2D Motion
3) An airplane flies 600 miles with a tail wind in 2.0 hrs. If it takes 2.5 hrs to
cover the same distance against the headwind, then what is the speed of
the plane in still air?
A) 270 mph
B) 300 mph
C) 240 mph
D) 330 mph
E) 250 mph
Main Idea 3 - Vectors and 2D Motion
4) The length of the vector = 5i + 12j is
A) 169 units
B) 144 units
C) 25 units
D) 17 units
E) None of these is correct.
Main Idea 3 - Vectors and 2D Motion
5) A projectile is fired at an angle of 45º above the horizontal. If air resistance
is neglected, the line in the graph that best represents the horizontal
displacement of the projectile as a function of travel time is
A) 1 B) 2 C) 3 D) 4
E) None of these is correct.
Main Idea 3 - Vectors and 2D Motion
6) Which of the following statements is not true of a projectile moving near
the surface of the earth against negligible air resistance?
A. The horizontal velocity is constant.
B. The vertical acceleration is constant.
C. The horizontal displacement is directly proportional to the time of flight.
D. The vertical velocity at any given time is independent of the angle of
projection.
E. The horizontal acceleration is constant.
Main Idea 3 - Vectors and 2D Motion
7) A stone with a mass m is dropped from an airplane that has a horizontal
velocity v at a height h above a lake. If air resistance is neglected, the
horizontal distance R from the point on the lake directly below the point of
release to the point where the stone strikes the water is given by which
formula?
A) R = v(2h/g)2
B) R = (1/2)gt2
C) R= 2mv(2h/g)½
D) R= v(2h/g)½
E) None of these is correct
Main Idea 3 - Vectors and 2D Motion
8) A golfer drives her ball from the tee down the fairway in a high arcing shot.
When the ball is at the highest point of its flight,
A)its velocity and acceleration are both zero.
B)its velocity is zero but its acceleration is nonzero.
C)its velocity is nonzero but its acceleration is zero.
D)its velocity and acceleration are both nonzero.
E)Insufficient information is given to answer correctly.
Main Idea 3 - Vectors and 2D Motion
9) The figure represents the parabolic trajectory of a ball going from A to E in
earth gravity but without air resistance. What is the direction of the
acceleration at point B?
A)It is up and to the right.
B) It is down and to the left.
C)It is straight up.
D) It is straight down.
E)The acceleration of the ball is zero.
Main Idea 3 - Vectors and 2D Motion
10)The figure represents the parabolic trajectory of a ball going from A to E.
What is the speed at point C compared with that at point A?
A)It is greater at C than at A.
B)It is less at C than at A.
C)The speeds are identical.
D)The speeds are both zero.
E)It is not possible to answer this
Main Idea 3 - Vectors and 2D Motion
Answers for questions in this section:
1) A
2) E
3) A
4) E
5) C
6) D
7) D
8) D
9) D
10) B
Main Idea 3 - Vectors and 2D Motion
If this is an area that gives you trouble use the following for additional support/practice.
Use the youtube channel “Lasseviren” for help
on specific topics/applications. You can search
the channel for specific topics. Not super fancy,
but great physics!
http://www.slideshare.net/Mrreynon/physics-chapter-3-powerpoint?related=1
Main Idea 4 - Forces
- Newton’s Laws of Motion
- NET FORCE
- Applications of 2nd Law
(understand them and their applications)
(Systems, Inclines, Atwoods, Elevators, Overheads, Equilibrium...lots of applications)
- Friction
(static v kinetic, maximum friction available v friction encountered, applications in problems)
- Centripetal Force
(Since we just finished this hopefully it is fresh in your mind - remember that FC is a NET force (Fnet = FC = mac)
and one (or more) force can act centripetally.
This chapter is HUGE...think about it, we spent an entire quarter talking about forces.
Main Idea 4 - Forces
1) A body moves with constant speed in a straight line. Which of the following
statements must be true?
A)No force acts on the body.
B)A single constant force acts on the body in the direction of motion.
C)A single constant force acts on the body in the direction opposite to the motion.
D)A net force of zero acts on the body.
E)A constant net force acts on the body in the direction of motion.
Main Idea 4 - Forces
2) A force accelerates a body of mass M. The same force applied to a
second body produces three times the acceleration. What is the mass of
the second body?
A) M B) 3M C) M/3 D) 9M E) M/9
Main Idea 4 - Forces
3) A mass of 25 kg is acted on by two forces: F1 is 15 N due east, and F2 is
10 N due north. The acceleration of the mass is
A. (15i + 10j) m/s2
B. (10i + 15j)m/s2
C. (0.4i + .6j)m/s2
D. (0.6i + 0.4j)m/s2
E. (.2i + 1j)m/s2
Main Idea 4 - Forces
4) A mass of 25 kg is acted on by two forces: 1 is 15 N due east, and 2 is 10 N
due north. The magnitude and direction of the acceleration of the mass is
A. 0.72 m/s2, 56.3º north of east.
B. 0.20 m/s2, due east.
C. 0.72 m/s2, 33.7º north of east.
D. 1.0 m/s2, 33.7º north of east.
E. 0.20 m/s2, 56.3º north of east.
Main Idea 4 - Forces
5) An object is moving to the right at a constant speed. Which one of the following
statements must be correct?
A)No forces are acting on the object.
B) A larger number of forces are acting on the object to the right than to the left.
C)The net force acting on the object is to the right.
D)No net force is acting on the object.
E)Just one force is acting on the object, and it is acting downward.
Main Idea 4 - Forces
6) A force F produces an acceleration a on an object of mass m. A force 3F is
exerted on a second object, and an acceleration 8a results. What is the mass
of the second object?
A) 3m B) 9m C) 24m D) (3/8)m E) (8/3)m
Main Idea 4 - Forces
7) A fat cat, ever conscious of its weight, walks into an elevator and steps on a
scale. The elevator begins to accelerate downward. While the elevator is
A)more than when the elevator is stationary.
B)more than if the elevator were accelerating upward.
C)less than when the elevator is stationary.
D)a negative value.
E)Insufficient information is given to answer correctly.
Main Idea 4 - Forces
8) The acceleration due to gravity on the moon is only about 1/6 of that on earth.
An astronaut whose weight on earth is 600 N travels to the lunar surface. His
mass as measured on the moon is
A) 600 kg
B) 100 kg
C) 61.2 kg
D) 10.0 kg
E) 360 kg
Main Idea 4 - Forces
9) A man pushes horizontally on the book with force and moves it at constant
speed along the table. Three "agents" exert forces on the book, shown as A, B
and C in the second diagram, and three "agents" exert forces on the table,
shown as D, E and F in the third diagram. The "action–reaction" forces of
Newton's third law are
A. C and F
B. D and F
C. A and D
D. A and F
E. D and E
Main Idea 4 - Forces
10)
Main Idea 4 - Forces
11)A box sits on an inclined plane without sliding. As the angle of inclination
increases, the normal force
A)increases.
B)decreases.
C)does not change.
D)is directed upward.
E)is directed in the direction of the gravitational force.
Main Idea 4 - Forces
12)A block is placed on a plane whose angle of inclination is 30º. The coefficients
of static and kinetic friction for the block on the inclined plane are both 0.2. The
block
A)remains stationary on the inclined plane.
B)accelerates down the inclined plane.
C)travels down the inclined plane at constant velocity.
D)travels up the inclined plane at constant velocity.
E)accelerates up the inclined plane.
Main Idea 4 - Forces
13)A 10-kg block is at rest on a level surface, where the coefficient of static friction
is 0.6 and that for kinetic friction is 0.4. A 50-N horizontal force is applied. The
frictional force on the block is
A) 20 N
B) 50 N
C) 40 N
D) 60 N
E) 10 N
Main Idea 4 - Forces
14)Which of the following statements is NOT true about friction?
A)µk is less than µs.
B)µk is independent of the relative speed of the surfaces
C)µk depends on the relative speed of the surfaces at speeds over several meters
per second.
D)The coefficients of friction depend on the nature of the surfaces.
E)The force of static friction depends on the area of contact between the two
surfaces.
Main Idea 4 - Forces
Main Idea 4 - Forces
Answers for questions in this section:
1) D
2) C
3) D
4) C
5) A
6) D
7) C
8) C
9) D
10) E
11)B
12)B
13)B
14) E
15) E
Main Idea 4 - Forces - some “mathier” stuff...
16)A car is accelerating at a rate of 2.5 m/s2. A mass of 250 g is hanging from
the ceiling on a string 1.2 m long. The angle that the string makes with the
vertical is
A)14.3º toward the back of the car.
B) 76º toward the back of the car.
C) 7º toward the front of the car.
D)14.3º toward the front of the car.
E) 0º, or straight down.
Main Idea 4 - Forces - some “mathier” stuff...
17)A burglar tries to escape the scene of a crime by sliding down a nylon
rope made by tying stockings together. The rope will withstand a
maximum tension of 300 N without breaking. Her mass is 61.2 kg. The
magnitude of the smallest acceleration a with which she can slide down
the rope is
A) 9.81 m/s2
B) 4.91 m/s2
C) zero
D) 2.40 m/s2
E) 19.6 m/s2
Main Idea 4 - Forces - some “mathier” stuff...
18)Two masses, m1 and m2, connected by a massless string, are accelerated
uniformly on a frictionless surface as shown. The ratio of the tensions 1/2 is
given by
A) m1/m2 B) m2/m1 C) (m1 + m2)/m2 D) m1/(m1 + m2) E) m2/(m1 + m2)
Main Idea 4 - Forces - some “mathier” stuff...
19)A mass m is hanging on a string that passes over a pulley and is then
attached to another mass 3m that is resting on a horizontal table. Neglect
friction. Mass m is held motionless and is then released. When it has fallen
a distance h, it will have a speed v which can be calculated from the formula
A) v= (gh/4)½
B) v= (gh/2)½
C)v= (gh)½
D)v= (2gh)½
E) none of these is correct
Main Idea 4 - Forces - some “mathier” stuff...
Main Idea 4 - Forces - some “mathier” stuff...
21)Two objects are sliding at the same speed across a wooden surface. The
coefficient of kinetic friction between the first object and the surface is twice that
between the second object and the surface. The distance traveled by the first
object before it stops is S. The distance traveled by the second object is
A) impossible to determine without knowing the masses involved.
B)2S
C)S/2
D)S
E)4S
Main Idea 4 - Forces - some “mathier” stuff...
22)A block of mass m is pulled in the direction shown in the figure across a
rough surface at a constant velocity. The magnitude of the frictional force is
A) µkmg
B) µkT cos q
C) µk(T – mg)
D) µkT sin q E) µk(mg – T sin q)
Main Idea 4 - Forces - some “mathier” stuff...
23) A mass M = 5.6 kg on a horizontal table is pulled by a horizontal string that
passes over a frictionless pulley to a free-hanging mass m = 3.4 kg. The
coefficient of friction between M and the table is 0.28. The acceleration of M
is
A) 3.7 m/s2
B) 2.0 m/s2
C) 2.2 m/s2
D) 0.20 m/s2
E) 0.49 m/s2
Main Idea 4 - Forces - some “mathier” stuff...
24)A block of mass M is sliding down a rough inclined surface that makes an
angle q with respect to the horizontal. If the coefficient of static friction is us
and kinetic friction uk, then the acceleration of the block down the incline is
equal to:
A)gsinq - guscosq
B)gcosq - gukcosq
C)guscos q - gsinq
D)gsinq - g ukcosq
E) gsinq - guscosq - gukcosq
Main Idea 4 - Forces
Answers for questions in this section:
16) A
17) B
18) D
19) B
20) D
21) B
22) E
23) B
24) A
Main Idea 4 - Forces - Drag and UCM
25)When a particle moves in a circle with constant speed, its acceleration is
A)constantly increasing.
B)constant in direction.
C)zero.
D)constant in magnitude.
E)constant in magnitude and direction.
26)A car going around a curve of radius R at a speed V experiences a
centripetal acceleration ac. What is its acceleration if it goes around a
curve of radius 3R at a speed of 2V?
A) (2/3)ac B) (4/3)ac C) (2/9)ac D) (9/2)ac E) (3/2)ac
Main Idea 4 - Forces - Drag and UCM
27) An object traveling in a circle at constant speed
A)is moving with constant velocity.
B)may be slowing down or picking up speed.
C)experiences no acceleration.
D)experiences an acceleration toward the center of the circle.
E)is described by none of the above statements.
28) A car experiences both a centripetal and a tangential acceleration. For which of the
following would this be true?
A)It is going around a curve at a constant speed.
B)It is going around a curve and slowing down.
C)It is going along a straight road at a constant speed.
D)It is going along a straight road and increasing its speed.
E)It is going along a straight road and decreasing its speed.
Main Idea 4 - Forces - Drag and UCM
29) The figure shows a top view of a ball on the end of a string traveling
counterclockwise in a circular path. The speed of the ball is constant. If the string
should break at the instant shown, the path that the ball would follow is
A) 1 B) 2 C) 3 D) 4 E) impossible to tell from the given information
Main Idea 4 - Forces - Drag and UCM
30)An object with a mass of m = 12.0 g is falling through a resistive fluid in
which g is constant. The retarding frictional force due to the fluid is F = bv,
where F is the force in newtons, b is a constant, and v is the speed in
meters per second. If F = 3.2 x10–2 N when v = 16.0 m/s, the terminal
speed of the object falling through the fluid is
A. 0.12 m/s
B. 59 m/s
C. 0.19 km/s
D. 16.0 m/s
E. None of these is correct.
Main Idea 4 - Forces - Drag and UCM
31)As a skydiver falls through the air, her terminal speed
A)depends on her mass.
B)depends on her body's orientation.
C)depends on the local value of the acceleration due to gravity.
D)depends on the density of the air.
E)is described by all of the above.
Main Idea 4 - Forces - Drag and UCM
Answers for questions in this section:
25) D
26) B
27) D
28) B
29) B
30) B
31) E
Main Idea 4 - Forces
If this is an area that gives you trouble use the following for additional support/practice.
Use the youtube channel “Lasseviren” for help
on specific topics/applications. You can search
the channel for specific topics. Not super fancy,
but great physics!
http://www.slideshare.net/Mrreynon/chapter-4-powerpoint-presentation?next_slideshow=1
aws
Main Idea 5 - Application of Calculus
As you noticed (and hopefully remember) we
often use calculus to help us describe
quantities in physics.
You should be comfortable with the concepts
and applications of:
- derivatives (slope of tangent line)
- integrals (area beneath curve)
- unit vector notation and multiplication
Main Idea 5 - Application of Calculus
You should be comfortable with the concepts
and applications of:
- derivatives (slope of tangent line) The notes for derivatives and
integrals are still posted on our
- integrals (area beneath curve)
class webpage.
- unit vector notation and multiplication
You can also visit YouTube for help (again Lasseviren 1 and do a search for
Unit Vectors or derivatives & antiderivatives)
Semester Exam Format
Part 1- Free Response
2 full (15 point) FR Questions
2 partial (10 point) FR Questions
You will be permitted to use your equation sheets and calculators for 45 minutes on this section
Part 2 - Multiple Choice
20 questions (theory and “quick” calculation)
You will NOT be permitted to use your equation sheets or your calculators for the rest of the exam time.
This is shorter than a normal AP test (and covers less material) - you should not be pressed for time.
That’s it…
This is not a “memorize and do well” test (or
class for that matter). You will have to apply
what you have learned, not just recreate
scenarios which you have already done.
THINK and Good Luck!
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