Module 2, Recitation 2

Concept questions on v-t graphs

ConcepTest Graphing Velocity I

t

x

The graph of position versus The graph of position versus

time for a car is given below. time for a car is given below.

What can you say about the What can you say about the

velocity of the car over time?velocity of the car over time?

1) it speeds up all the time

2) it slows down all the time

3) it moves at constant velocity

4) sometimes it speeds up and

sometimes it slows down

5) not really sure

ConcepTest Graphing Velocity I

t

x

The graph of position versus The graph of position versus

time for a car is given below. time for a car is given below.

What can you say about the What can you say about the

velocity of the car over time?velocity of the car over time?

The car moves at a constant velocity

because the x vs. t plot shows a straight

line. The slope of a straight line is

constant. Remember that the slope of x

versus t is the velocity!

1) it speeds up all the time

2) it slows down all the time

3) it moves at constant velocity

4) sometimes it speeds up and

sometimes it slows down

5) not really sure

t

x

1) it speeds up all the time

2) it slows down all the time

3) it moves at constant velocity

4) sometimes it speeds up and

sometimes it slows down

5) not really sure

The graph of position vs. The graph of position vs.

time for a car is given below. time for a car is given below.

What can you say about the What can you say about the

velocity of the car over time?velocity of the car over time?

ConcepTestConcepTest Graphing Velocity IIGraphing Velocity II

1) it speeds up all the time

2) it slows down all the time

3) it moves at constant velocity

4) sometimes it speeds up and

sometimes it slows down

5) not really sure

t

x

The graph of position vs. The graph of position vs.

time for a car is given below. time for a car is given below.

What can you say about the What can you say about the

velocity of the car over time?velocity of the car over time?

The car slows down all the time

because the slope of the x vs. t graph is

diminishing as time goes on.

Remember that the slope of x vs. t is

the velocity! At large t, the value of the

position x does not change, indicating

that the car must be at rest.

ConcepTestConcepTest Graphing Velocity IIGraphing Velocity II

Consider the Consider the vv versus versus tt

plot. How does the plot. How does the

speed change with time?speed change with time?

v

t

1) decreases1) decreases

2) increases2) increases

3) stays constant3) stays constant

4) increases, then decreases4) increases, then decreases

5) decreases, then increases5) decreases, then increases

ConcepTestConcepTest vv versus versus tt graphs I graphs I

Consider the Consider the vv versus versus tt

plot. How does the plot. How does the

speed change with time?speed change with time?

v

t

1) decreases1) decreases

2) increases2) increases

3) stays constant3) stays constant

4) increases, then decreases4) increases, then decreases

5) decreases, then increases5) decreases, then increases

The initial velocity is positive and the magnitude of the velocity continues to increase with time.

ConcepTestConcepTest vv versus versus tt graphs I graphs I

Consider the Consider the vv versus versus tt

plot. How does the plot. How does the

speed change with time?speed change with time?

v

t

1) decreases1) decreases

2) increases2) increases

3) stays constant3) stays constant

4) increases, then decreases4) increases, then decreases

5) decreases, then increases5) decreases, then increases

ConcepTestConcepTest vv versus versus tt graphs II graphs II

Consider the Consider the vv versus versus tt

plot. How does the plot. How does the

speed change with time?speed change with time?

v

t

1) decreases1) decreases

2) increases2) increases

3) stays constant3) stays constant

4) increases, then decreases4) increases, then decreases

5) decreases, then increases5) decreases, then increases

The initial velocity is positive but the

magnitude of the velocity decreases

toward zero. After this, the magnitude

increases again, but becomes negative,

indicating that the object has changed

direction.

ConcepTestConcepTest vv versus versus tt graphs II graphs II

ConcepTest Rubber Balls Iv

t1

v

t2

v

t3v

t4

You drop a rubber ball. Right after it You drop a rubber ball. Right after it

leaves your hand and before it hits the leaves your hand and before it hits the

floor, which of the above plots floor, which of the above plots

represents the represents the v v vs.vs. t t graph for this graph for this

motion? (Assume your y-axis is motion? (Assume your y-axis is

pointing up).pointing up).

ConcepTest Rubber Balls Iv

t1

v

t2

v

t3v

t4

You drop a rubber ball. Right You drop a rubber ball. Right

after it leaves your hand and after it leaves your hand and

before it hits the floor, which of before it hits the floor, which of

the above plots represents the the above plots represents the

v v vs.vs. t t graph for this motion? graph for this motion?

(Assume your y-axis is pointing (Assume your y-axis is pointing

up).up).

The ball is dropped from rest, so its

initial velocity is zeroinitial velocity is zero. Since the y-axis

is pointing upwards and the ball is

falling downwards, its velocity is velocity is

negativenegative and becomes more and more more and more

negativenegative as it accelerates downward.

v

t4

v

t2

v

t3

v

t1

You toss a ball straight up in the air You toss a ball straight up in the air

and catch it again. Right after it and catch it again. Right after it

leaves your hand and before you catch leaves your hand and before you catch

it, which of the above plots represents it, which of the above plots represents

the the v v vs.vs. t t graph for this motion? graph for this motion?

(Assume your y-axis is pointing up).(Assume your y-axis is pointing up).

ConcepTestConcepTest Rubber Balls II

v

t4

v

t2

v

t3

v

t1

You toss a ball straight up in You toss a ball straight up in

the air and catch it again. the air and catch it again.

Right after it leaves your hand Right after it leaves your hand

and before you catch it, which and before you catch it, which

of the above plots represents of the above plots represents

the the v v vs.vs. t t graph for this graph for this

motion? (Assume your y-axis motion? (Assume your y-axis

is pointing up).is pointing up).

The ball has an initial velocity that is initial velocity that is

positivepositive but diminishing as it slows. It

stops at the top (v = 0), and then its

velocity becomes negativevelocity becomes negative and

becomes more and more negativemore and more negative as it

accelerates downward.

ConcepTestConcepTest Rubber Balls II

v

t1

v

t2

v

t3v

t4

ConcepTestConcepTest Rubber Balls III

You drop a very bouncy rubber You drop a very bouncy rubber

ball. It falls, and then it hits the ball. It falls, and then it hits the

floor and bounces right back up to floor and bounces right back up to

you. Which of the following you. Which of the following

represents the represents the v v vs.vs. t t graph for graph for

this motion?this motion?

v

t1

v

t2

v

t3v

t4

You drop a very bouncy rubber You drop a very bouncy rubber

ball. It falls, and then it hits ball. It falls, and then it hits

the floor and bounces right the floor and bounces right

back up to you. Which of the back up to you. Which of the

following represents the following represents the v v vs.vs.

tt graph for this motion? graph for this motion?

Initially, the ball is falling down, so its velocity must be negativenegative (if UP is positive). Its velocity is also increasingincreasing in magnitude as it falls. Once it bounces, it changes direction and then has a

positivepositive velocity, which is also

decreasingdecreasing as the ball moves upward.

ConcepTestConcepTest Rubber Balls III

Module 2, Recitation 2

Match the s-v-a vs. t graphs of Pasco car motion

Track 1: Level track, spring plunger on one end and Velcro on the other. Start the car in the center of the track and give it a gentle push towards the end with the plunger. Plot graphs for the motion from when you finish pushing the car until it stops.

Insert graph from Data Studio of position-velocity-acceleration

Track 2: Level track, fan accessory. Start car at left end. The fan is set to be on for 1 second. Plot graphs for the motion from when the fan starts until the car reaches the right end of the track.

Insert graph from Data Studio of position-velocity-acceleration

Track 3: Inclined track, spring plunger. Let the car roll down the track and bounce off the end several times.

Insert graph from Data Studio of position-velocity-acceleration

Track 4: Inclined track; small, and large sails. Plot the motion from when released until the car reaches the end of the track. Compare motion for no sail (track 3), the small sail, and the large sail.

Insert graph from Data Studio of position-velocity-acceleration

Module 2, Recitation 2

Match the amusement park acceleration graphs

Mr Hyde

Time

Ac

ce

lera

tio

n

C

Bounty

TimeA

cc

ele

rati

on A

Double Loop

TimeA

cc

ele

rati

on D

Superman Ultimate Escape

Time

Ac

ce

lera

tio

n

F

Villain

TimeA

cc

ele

rati

on B

Drop Zone

Time

Ac

ce

lera

tio

n E