Conceptual Physics

1
Conceptual Physics

• Motion Review
• Pre-Test Activity

2

• Answer a series of questions as review for the
  chapter to the best of your ability
• You will immediately grade your own this is not
  going to be for a grade, so be honest this is
  only to help you prepare for the test
• After grading each of the questions, you will
  assess which areas you need to work on.
• Then we will take another quiz, over the same
  type of material and see how you did. Again this
  will not be for a grade

3

• 1) An object is thrown straight up in the air
  with an initial speed of 20 m/s, how long will
  it take to get to its highest point?
• 2) What is its instantaneous speed at its
  highest point?
• 3) What is its acceleration as soon as it leaves
  the persons hand?
• 4) What is its acceleration at its highest
  point?
• 5) How long will it take to land back in the
  hand (assuming it is at the same height) ?

4
Answers for 1-5

• 1) 2 seconds
• 2) 0 m/s
• 3) -10 m/s2
• 4) -10 m/s2
• 5) 4 seconds

5

• A cop car at rest views Car A headed East at a
  speed of 40 mph, and then views Car B headed
  West (towards Car A) moving at 60 mph.
• 6) What is the speed of Car B relative to Car A?
• 7) If they were moving in the same direction
  with Car B ahead of Car A, what would be the
  speed of Car B relative to Car A ?

6

• Answers 6-7
• 6) 100 mph
• 7) 20 mph

7

• 8) Does a speedometer in a car tell you
  instantaneous speed or average speed?
• 9) True or false? When an object is travelling
  at a constant speed, the instantaneous speed is
  equal to the average speed at all points.
• 10) True or false? The slope of a
  displacement-time graph is equal to acceleration?

8
Answers 8-10

• 8) instantaneous
• 9) true
• 10) false

9

• 11) A freely falling object starts from rest.
  After falling for 3 seconds what will be its
  velocity?
• 12) If you drop a feather and a coin at the same
  time in a vacuum tube (place with no air), which
  will reach the bottom of the tube first?

10
Answers 11-12

• 11) -30 m/s
• 12) both will hit at the same time

11

• 13) What is the acceleration of a car that takes
  4 sec. to go from 4 m/s to 40 m/s?
• 14) What is that same cars average velocity?

12
Answers 13-14

• 13) 9 m/s2
• 14) 22 m/s

13

• 15) A jet can be launched from 0 to 90 m/s in 3
  seconds. A) What is the acceleration of the jet?
  B ) If the acceleration is constant, what is
  the average velocity of the jet?

• What is the average speed of
• a cat that runs a distance of 40m
• in 5 seconds?

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• 15) 30 m/s2 , 45 m/s
• 16) 8 m/s

15
24
V (m/s)
4
t (s)

• 17) Using the above graph describe what type of
  motion is going on (constant velocity,
  acceleration, or not moving)
• 18) Using the numbers on the graph what was the
  acceleration?
• 19) What was the average velocity?
• 20) if you remember displacement is always equal
  to AVERAGE velocity multiplied by time, so what
  was the total displacement of the object?

16
Answers 17-20

• 17) Acceleration
• 18) 6 m/s2
• 19) 12 m/s
• 20) 48 m

17
64
d (m)
4
t (s)

• 21) Describe what type of motion this graph is
  showing (constant velocity, not moving, or
  acceleration)
• 22) What is the average velocity of this graph?
• 23) What is the instantaneous velocity at time
  2 seconds?
• 24) What is the acceleration of this graph?

18
Answers 21-24

• 21) Constant speed
• 22) 16 m/s
• 23) 16 m/s
• 24) 0 m/s2

19
V (m/s)

t (s)

• 25) What type of motion is being shown here??
  (constant speed, acceleration, or at rest)

20
d (m)
t (s)

• 26) What type of motion is being shown here??
  (constant velocity , at rest, or acceleration)

21
Answers 25-26

• 25) constant speed
• 26) at rest

22

• 27) How is velocity different than speed?
• 28) give two possible units for velocity?

23

• 27) velocity has a direction, speed does not
• 28) m/s, km/hr , mph .

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Pre-Test 2
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• 1) An baseball is thrown straight up in the air
  with an initial speed of 40 m/s, how long will
  it take to land back in the persons hand?
• 2) What is its acceleration at its highest
  point?
• 3) What is its acceleration as soon as it leaves
  the persons hand?
• 4) What is its speed at its highest point?
• 5) What will be the speed and direction of the
  object after 3 seconds?

26
Answers for 1-5

• 1) 8 seconds
• 2) 10 m/s2 down
• 3) 10 m/s2 down
• 4) 0 m/s
• 5) 10 m/s up

27

• A cop car at rest views Car A headed East at a
  speed of 50 mph, and then views Car B towards
  Car A moving at 65 mph.
• 6) What is the speed of Car B relative to Car A?
• 7) If they were moving in the same direction
  with Car B ahead of Car A, what would be the
  speed of Car B relative to Car A ?

28

• Answers 6-7
• 6) 115 mph
• 7) 15 mph

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• 8) Does dividing the amount of miles you drove
  during a trip by the total time of the trip give
  you your average speed, or your instantaneous
  speed?
• 9) True or false? When an object accelerating,
  the instantaneous speed is equal to the average
  speed at all times.
• 10) True or false? The slope of a velocity-time
  graph is equal to acceleration?

30
Answers 8-10

• 8)average
• 9) false
• 10) true

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• 11) A freely falling object starts from rest.
  After falling for 9 seconds what will be its
  speed? (ignore air resistance)
• 12) If you drop a feather and a coin at the same
  time in air which will reach the bottom of first?
  WHY?

32
Answers 11-12

• 11) 90 m/s
• 12) coin because too much air resistance

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• 13) What is the acceleration of a car that takes
  7 sec. to go from 5 m/s to 47 m/s?
• 14) What is that same cars average speed?

34
Answers 13-14

• 13) 6 m/s2
• 14) 26 m/s

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• 15) A jet can be slowed down from 75 m/s to 0
  m/s in 5 seconds. What is the acceleration of
  the jet?
• 16) What is the average speed of a cheetah that
  runs a distance of 100m in 5 seconds?

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• 15) -15 m/s2
• 16) 20 m/s

37
36
V (m/s)
3
t (s)

• 17) Using the above graph describe what type of
  motion is going on (constant speed, acceleration,
  or not moving)
• 18) Using the numbers on the graph what was the
  acceleration?
• 19) What was the average velocity?
• 20) if you remember displacement is always equal
  to AVERAGE velocity multiplied by time, so what
  displacement did the object in the graph travel?

38
Answers 17-20

• 17) Acceleration
• 18) -12 m/s2
• 19) 18 m/s
• 20) 54 m

39
28
d (m)
4
t (s)

• 21) Describe what type of motion this graph is
  showing (constant speed, not moving, or
  acceleration)
• 22) What is the average velocity of this graph?
• 23) What is the instantaneous velocity at time
  3 seconds?
• 24) What is the acceleration of this graph?

40
Answers 21-24

• 21) Constant speed
• 22) 7 m/s
• 23) 7 m/s
• 24) 0 m/s2

41
V (m/s)

t (s)

• 25) What type of motion is being shown here??
  (constant speed, acceleration, or at rest)

42
d (m)
t (s)

• 26) What type of motion is being shown here??
  (constant speed, at rest, or acceleration)

43
Answers 25-26

• 25) constant speed
• 26) constant speed

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• 27) How can you change the velocity of an object
  without changing its speed?
• 28) give two possible units for distance?

45

• 27) by changing direction. While still
  maintaining the same speed
• 28) m , km , miles

46
Random Questions

• What advantage does skydiving from such a high
  altitude, as they are in the RedBull Stratos
  project, have in terms of speed?

47

• Skydiver can reach much higher speeds at high
  altitude b/c at a High altitude there is much
  less air which means much less air resistance to
  slow the skydiver down.

48

• How is it possible that Knight Rider could drive
  his car up the back of that semi-trailer while it
  was moving down the highway?

49

• Car has low speed relative to truck and as soon
  as car is on truck, it will keep the same speed
  relative to truck

50

• In the Jamiroqui music video why does it look
  like the floor is moving?

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• We watch it from the perspective of the
  camera/walls, so looks like floor is moving when
  camera/walls are actually moving.

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• If Usain Bolts average speed during the 100 m
  dash is 10.3 m/s, is it likely that he reached
  instantaneous speeds higher than this during the
  race?

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• Yes, he started from rest so the low speeds in
  the beginning bring down his average speed. When
  he is at top speed, instantaneous speed is much
  higher than the average.

54

• In the movie Speed, Keanu Reeves character
  jumped from a car travelling at 52 mph to a bus
  travelling at 52 mph right along side it. This
  was possible because the cars speed relative to
  the truck was_______.

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• 0 mph
• They have no speed relative to each other, so
  its just like jumping from one motionless car to
  another one

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What does the symbol ? mean?
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Change in

• Seen in the equation for Acceleration
• a ?v/ t

58

• During the RedBull Stratos project, skydiver
  Felix Baumgartner is supposed to be the first
  human to break the sound barrier during free
  fall. If the speed of sound is 340 m/s and he
  falls from rest at an extremely high altitude,
  about how long will it take him to reach the
  speed of sound?

59

• About 34 seconds
• Will not get slowed down by air b/c at a high
  altitude
• Will gain about 10 m/s of velocity every second
  due to gravity.