Motion (Part - 2)- Class 9 Science Test, 21-02-2018 - Class 9 MCQ

In the distance-time graph shown above, the speed of object A is greater than speed of object B as the object A is covering more distance per unit time.

The reference point for measuring position of a body is called origin. Every distance is measured in respect to origin.

When a body does not change its position with respect to time, it is said that body is in state of rest. Rest and motion are relative to observer.

The magnitude of average velocity of an object is equal to its average speed when body is moving with uniform motion, having constant acceleration and body moves in straight path without changing its direction.

A person sitting in the truck projected a ball vertically upwards. The ball will fall back in his hand as the ball and the truck are moving with same speed.

In displacement time graph, if the graph is curved line than the motion of the body is non-uniform as unequal distance is travelled in equal interval of time.

Initial velocity (u) = 90 km/h = 90×5/1890×5/18=25 m/s, a = -0.5m/s2. V = 0m/s. 2as = V2-u2, S = V2-u2/ 2a = 252 – 02/ 2×0.52×0.5= 625/1 = 625 m.

First equation of motion is v = u + at, so, in first equation of motion displacement is not present.

When a body moves with constant speed its acceleration is not acting. The body is said to be accelerating if it moves in a uniform circular motion. The slope of velocity-time graph gives instantaneous acceleration.

The third equation of motion is v2 = u2 + 2aS, where, V = final velocity, u= initial velocity, a = acceleration and s= displacement.

Here, initial velocity (u) = 0 m/s, final velocity (v) = 144 km/h =144 x 5/18= 40 m/s, t = 20s, a = 40-0/20 = 2 m/s² .

S= ut + ½ at² = 0×20+1/2×2×20×20=400m

The motion of the athletes in a straight line and uniform circular motion both are the case of accelerated motion. In both cases speed increase with time.

Scalar- A physical quantity having only magnitude is known as a scalar quantity. A scalar quantity has no direction.

Vector- A physical quantity having a magnitude as well as direction is known as vector quantity.

Circular motion -Motion about a fixed point called as centre. In other words,motion in a circle is circular motion.

Rectilinear motion- Rectilinear motion is another name for straight-line motion. This type of motion describes the movement of a particle or a body. 

Acceleration of a body is defined as the rate of change of its velocity with time.

Velocity of a body is defined as the rate of change of its displacement with time.

Speed of a body is the distance travelled by it per unit time.

When a body moves along a circular path,then its direction of motion keeps changing continuously.Therefore,the motion along a circular path is said to be accelerated.

The speed of a running vehicle at any instant of time is shown by an instrument called 'speedometer'. The distance travelled by a vehicle is measured by another instrument called 'odometer' which is installed in the vehicle.It records the distance in kilometres.

The area occupied in the velocity-time graph is used to calculate displacement of the body.

CGS unit of velocity is cm/s and SI unit of velocity is m/s.

Ratio of CGS unit to SI unit= cm/m

(1 meter is equal to 100 cm. )

Therefore, ratio = 1/100 = 1: 100

The nature of the distance-time graph for uniform motion of an object is straight line inclined to distance axis.

Vector- A physical quantity having a magnitude as well as direction is known as vector quantity.
Odometer- an instrument for measuring the distance travelled by a wheeled vehicle.

Acceleration of a body is defined as the rate of change of its velocity with time.

Scalar- A physical quantity having only magnitude is known as a scalar quantity.

Distance is the actual length covered by a body and displacement is the shortest distance between initial and final position. So, distance will be equal or more than displacement.

In distance-time graph, when graph is a straight line parallel to time axis is represented by object moving with constant speed without any acceleration.

General formula of the quantities acceleration,speed,average velocity, and third equation of motion are given.

Velocity of a body is defined as the rate of change of its displacement with time,

Acceleration of a body is defined as the rate of change of its velocity with time,

The average velocity is given by the "arithmetic mean" of the initial and final velocity for a given period of time,that is: Average velocity, 

Third equation of motion:v²=u²+2aS⟹v²−u²=2aS

A body starting from rest and when it comes to rest has velocity equal to zero.

A body moving with uniform velocity has zero acceleration since there is no change in velocity.

A body under free fall has an acceleration of 9.8 ms^-2

Non-uniform motion - A body has a non-uniform motion if it travels unequal distances in equal intervals of time.
Speed from distance-time graph- The distance-time graph of a body can be used to calculate the speed of the body.The slope of a distance-time graph indicates speed.
Distance covered from speed-time graph - The distance travelled bya moving body in a given time can be calculated from its speed-time graph.Area enclosed by the speed-time graph with the X-axis gives the distance covered.
Average velocity -If the velocity of a body is always changing,but changing at a uniform rate,then the average velocity is given by the "arithmetic mean" of the initial and final velocity for a given period of time,that is: 
Average velocity =