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# Basics of Physics

DISTANCE

It is the total length travelled by a body in its course of journey.

Characteristics of distance are:

• It is a scalar quantity.
• In CGS system, its unit cm (centimeter).
• In MKS system, its unit is m (meter).

DISPLACEMENT

The shortest distance between the initial and the final states of a body in its journey measured in a particular direction.

Characteristics of displacement are:

• It is a vector quantity.
• DISTANCE and DISPLACEMENT have same units.
• In CGS system, its unit cm (centimeter).
• In MKS system, its unit is m (meter).

DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT

If a body travels in a straight line, the distance and displacement will be equal.

However, if it does not then it can be explained with the help of following figure:

In the above figure, the curved distance from point A to B is the actual distance covered by the body and the shortest distance between A and B shown by a straight line is known as displacement.

SPEED

The rate of change of distance of a body in its journey is called speed

Characteristics of speed are:

• It is a scalar quantity.
• Its formula is, speed= distance/ time
• In CGS system, its unit is cm/sec.
• In MKS system, its unit is m/sec.

VELOCITY

The rate of change of displacement of a body in its journey is called velocity.

Characteristics of velocity are:

• It is a vector quantity.
• Speed and velocity have same units.
• In CGS system, its unit is cm/sec.
• In MKS system, its unit is m/sec.

DIFFERENCE BETWEEN SPEED AND VELOCITY

Suppose A body started moving in a circular direction from point A and covered the entire perimeter of 500 m in 20 sec and reached finally to the same origin point. Then speed will be calculated as

Speed= 500/20 = 25 m/sec

But, its velocity will be 0 as there is no change in the displacement and the initial point and the final point are the same. Thus, change in displacement will become 0 as a result velocity will become zero.

ACCELERATION

The rate of change of velocity of a body during its journey is called acceleration.

Characteristics of Acceleration are:

• Acceleration, a= change of velocity/ time
• When a body is moving with uniform velocity, then its acceleration will be zeto.
• In CGS system, its unit is cm/sec
• In MKS system, its unit is m/sec2
• It is a vector quantity.

Q.1. A bike accelerates uniformly from rest to a speed of 7.10 m/sec over a distance of 35.4 m. Determine the acceleration of the bike.

1. 0.712 m/sec2
2. 0.711 m/sec2
3. 0.710 m/sec2
4. 0.600 m/sec2

Ans. a

Q.2. A car takes 4 hours to cover a distance, if it travels with a speed of 40 mph. What should be its speed to cover the same distance in 1.5 hours:

1. 106.66 mph
2. 107 mph
3. 106 mph
4. 107.5 mph

Ans. a 