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# Class IX - Physics: Motion

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## Anshul Gupta

on 27 September 2014

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#### Transcript of Class IX - Physics: Motion

Motion
"Change of position with time"
Distance Vs Displacement
Distance or Displacement?
Distance = ................
Displacement = ..................
Distance Vs Displacement
Distance
Displacement
Exercise
Q1: A man travels 20 m to the north; then turns east and travels 30m after which he again turns north and covers another 20m. What is the Distance he covered? What was his displacement?

Exercise
Q2: A person moved along the following path from point A to B; point B to C and then point C to A.
What is the Distance Traveled?
What is the Displacement?
Uniform & Non-Uniform Motion
A body traveling equal distance in equal time intervals (no matter how small or large these intervals are)
Example????
Uniform Motion
Non Uniform Motion
Unequal distance in equal time intervals
Uniform Motion
Non Uniform Motion
Example????
Speed
Distance travelled per unit time
Speed =
Distance
Time
Average Speed
Average Speed =
Total Distance Traveled
Total Time Taken
DO NOT confuse this with “Uniform Speed”
Exercise
Q3: A cyclist covers a distance of 5 KM in 15 minutes. What is his speed in:
- Kilometer per hour
- Meter per second

Exercise
Q4: Vikas drives 180KM in 3 hrs while Vipin drives 150KM in 2.5 hrs. Who drives faster?
Exercise
Q5: A car travels first 5 km at 20km/h and the next 5 km at 30 km/h. What is its average speed?
Exercise
Q6: On a 120 km track, a train travels the first 30 km at a uniform speed of 30 km/h. How fast must the train travel the next 90 km so as to average 60 km/h for the entire trip?
Units???
Unit ???
Distance & Displacement
Uniform & Non-uniform
Motion

Speed
Velocity
Velocity =
Distance Traveled in a given direction
Time Taken
Distance traveled per unit time in a given direction
Velocity =
Displacement
Time Taken
or
Unit???
Uniform Velocity
If a body travels in a specific direction in straight line and moves over equal distances in equal intervals of time
The velocity fo the body can be changed by:
1. by changing the speed of the body, and
2. by changing the direction
Exercise
Q. Usha swims in a 90 m long pool. She covers 270 m in one minute by swimming back and forth from one end to the other along the same straight path. Find the average speed and average velocity of Usha.
Exercise
Q. A bus covers a distance of 250 km from Delhi to Chandigarh towards north in 4 hrs in the morning. In the evening it returns back to Delhi in 6 hrs. Find the average speed and average velocity for the whole journey.
Acceleration
Acceleration =
Change in velocity
Time Taken for change
Rate of change of velocity in unit time
Acceleration =
Final velocity - Initial velocity
Time taken
=
v - u
t
Unit???
Uniform Acceleration
Velocity increases or decreases by equal amounts in equal intervals of time
Examples???
Retardation /Deceleration / Negative Acceleration
If the velocity of the body decreases, the acceleration in negative.
final velocity < initial velocity
Retardation is acceleration with a negative sign
Exercise
Q. Starting from a stationary position, Rahul paddles his bicycle to attain a velocity of 6 m/s in 30 sec. Then he applies brakes such that the velocity of the bicycle comes down to 4 m/s in the next 5 sec. Calculate the acceleration of the bicycle in both the cases.
Exercise
Q. A train starting from a railway station and moving with uniform acceleration attains a speed 40 km/h in 10 minutes. Find its acceleration.
Exercise
Q. A bus decreases its speed from 80 km/h to 60 km/h in 5 sec. Find the acceleration of the bus.
Equations of Motions
First Equation of Motion
Second Equation of Motion
Third Equation of Motion
First Equation of Motion
v = u
+
at
v
= final velocity
u
= initial velocity
a
= acceleration
t
= time taken
Second Equation of Motion
s = ut + ½ at
s
= distance travelled
u
= initial velocity
a
= acceleration
t
= time taken
*for uniformly accelerated motion
2
Third Equation of Motion
v = u + 2as
v
= final velocity
u
= initial velocity
s
= distance traveled
a
= acceleration
2
2
Important Points
1. if a body starts from rest, its initial velocity,
u
= 0
2. if a body comes to rest (it stops), its final velocity,
v
= 0
3. if a body moves with uniform velocity, its acceleration,
a
= 0
Exercise
Q. A train starting from rest attains a velocity of 72 km/h in
5 minutes. Assuming that the acceleration is uniform, find (i) the acceleration and (ii) the distance traveled by the train for attaining this velocity.
Exercise
Q. A car accelerates uniformly from 18 km/h to 36 km/h in 5 sec. Calculate (i) the acceleration and (ii) the distance covered by the car in that time.
Exercise
Q. The brakes applied to a car produce an acceleration of 6 m/s in the opposite direction to the motion. If the car takes 2 s to stop after the application of brakes, calculate the distance it travels during this time.
2
Exercise
Q. A racing car has a uniform acceleration of 4 m/s . What distance will it cover in 10 s after start?
2
Exercise
Q. A trolley, while going down an inclined plane, has an acceleration of 2 cm/s . What will be its velocity 3 s after the start?
2
Graphical Representation of Motion
Distance-Time Graph
Speed -Time Graph
Distance-Time Graph
Speed-Time Graph
Depict:
1. Uniform Speed
2. Non-uniform Speed

Calculate: Speed
Depict:
1. Constant Speed
2. Uniform Acceleration
3. Uniform Retardation
4. Non-Uniform Acceleration

Calculate: Distance, Acceleration
Exercise
a. What type of motion is rep. by OA, AB & BC
b. What is the acceleration of body during OA, BC
c. What is the distance traveled by body during OA, AB and BC
Exercise
Q. A car is moving on a straight line with uniform acceleration. The speed of the car at different times is as follows:
Draw a speed time graph by choosing a convenient scale. Determine from it:
1. acceleration of the car
2. the distance covered by the car in 50 sec.
Derive Equation of Motion by Graphical Method
Derive:
1. v = u + at
2. s = ut + 1/2 at
3. v = u + 2as
2
2
2
Uniform Circular Motion
An object moving in a circular path with uniform speed, the motion is called uniform circular motion
The motion with constant speed along a circular path is an example of an accelerated motion. Why?
Examples???
Velocity during Circular Motion
v = 2πr / t
v
= velocity
t
= time taken
Exercise
Q. A cyclist goes around a circular track once every 2 minutes. If the radius of the circular track is 105 meters, calculate his speed (π = 22/7)
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