Prepared by:

SITI FAIRUZ BINTI MOHD NOORL 20091002852

Acceleration & Deceleration

Previous Lesson…

Velocity

Displacement Distance

Speed

in a linear motion is the magnitude of

is the rate of change of

is the rate of change of

In a specified direction has the shortest magnitude of

Video…….

At the end of this lesson, student should be able to:- Define acceleration and

deceleration- State that a= v-u

t- Calculate acceleration and

deceleration.

Learning Outcome

60 kmh-1 100 kmh-1

Initial velocity , u = 60 kmh-1

Final Velocity , v = 100 kmh-1

Time, t = 5 s

What can you say about the velocity of the car?

Suppose the car was moving with an initial velocity of 12 ms-1 and takes 6s to stop.

Calculate its acceleration.

u = 12 ms-1

v = 0 ms-1

t = 6 s

a = v - u = -2 ms-2

t

So, we can say that the car accelerates at -2 ms-2 or

the car decelerates at 2 ms-2 .

How does acceleration relate to change of

velocity?

How does acceleration relate to change of

time?

What is acceleration?

Acceleration = Change in velocity

Time taken for the change

The car accelerates from an initial velocity, u, to a final velocity, v, in time, t.

The acceleration of the car is

a = v-u ms-1

t sVector quantitySI unit : ms-2

a positive

v positive

a negative

v negative

a negative

v positive

Direction of motion

Direction of motion

Direction of motion

Direction of motiona positive

v negative

Slows

down

Slows

down

Speeds

up

Speeds

up

We can analyse linear motion in a laboratory using a ticker timer

A

B

C

Direction of motion

What can you say about the velocity and

acceleration of the trolley in each case?

Distance between dots is the same. The trolley is moving with constant

velocity.

ADirection of motion

The distance between dots is increasing.The trolley is moving with increasing

velocity.It has a positive acceleration.Speeds up.

BDirection of motion

The distance between dots is decreasing.The trolley is moving with decreasing

velocity.It is decelerating.Slows down.

CDirection of motion

A sprinter runs from the starting line and achieves a velocity of 18ms-1 in 3s.

Calculate his acceleration.

Answer:

We know that:

u= 0ms-1 a = v-u

v= 18ms-1 t

t=3s = 18 - 0 ms-1

3 s

= 6 ms-2

A stationary car achieves a velocity of 40ms-1 in 10 seconds.

Calculate the acceleration of the car.

(Assume that the acceleration of the car is uniform throughout the journey).

Problem to solve…

Acceleration = Change of velocity

Time

= Final velocity – Initial Velocity

Time

= 40ms-1 – 0ms-1

10s

= 4ms-1

Answer..

At the end of this lesson, student should be able to:- Define acceleration and

deceleration- State that a= v-u

t- Calculate acceleration and

deceleration.

Learning outcome…

Read “Analysing Motion Graph”- (text book; page 28)

Do review questions (Exercise Book, page 107)

Homework….