 # Motion in One Dimension

## Physical quantities are the quantities that can be measured. There are two types of physical quantities- scalar and vector quantities. Scalar quantities are the quantities that have only magnitude for example length, time etc. Vector quantities are the quantities that have magnitude as well as direction for example velocity, acceleration etc. Rest is the state of an object in which it does not change its position with respect to its surroundings and time. An object is said to be in motion when it changes its position with respect to time and surroundings. When an object moves on straight line path then its motion is said to be one dimensional. Distance is the actual path covered by an object. It can never be negative. Displacement is the shortest path between initial and final position of an object. It can be positive, negative and zero. Speed is the distance covered by an object per unit time. Speed is a scalar quantity. Speed of a body at any instant of time is known as instantaneous speed. Velocity is the displacement covered by an object per unit time. Velocity is a vector quantity. Acceleration is the rate of change of velocity. There are two types of acceleration -Positive and Negative acceleration. When an object describes equal change in velocity in equal interval of time then its acceleration is said to be uniform. The acceleration gained by an object due to gravitational force is known as acceleration due to gravity.

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• Q1

Which graph shows the variable velocity and uniform acceleration? Marks:1

Graph (ii) shows, the variable velocity and uniform acceleration.

• Q2

What do you understand by the term acceleration due to gravity?

Marks:1

The acceleration of a freely falling body, under the action of gravity of the earth is called acceleration due to gravity.

• Q3

Define instantaneous velocity.

Marks:1

The velocity possessed by a moving body at some particular instant is called instantaneous velocity.

• Q4

Define average velocity.

Marks:1

Average velocity is the ratio of the total distance travelled in specified direction to the total time taken by the body to cover that distance.

Thus, average velocity 