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# Velocity and Acceleration

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Velocity:

Velocity of an object is defined as the speed of an object moving in a definite direction. Velocity of an object can be uniform or variable. It can be changed by changing the object’s speed, direction of motion or both.

When an object is moving along a straight line at a variable speed, the magnitude of an object with its rate of motion is described in terms of average velocity.

SI unit of velocity – meter/second

Average velocity – initial velocity + final velocity

2

Mathematically, Vm = u + v

2

Where, Vm = average velocity

u = initial velocity

v = final velocity

During uniform motion, velocity remains constant with time and change in velocity for any time interval is zero.

During non-uniform motion, velocity varies with time. It has different values at different instants and at different points of the path. Hence the change in velocity of the object during any time interval is not zero.

Acceleration:

The rate of change in the velocity of an object per unit time is referred as acceleration and the kind of motion is known as accelerated motion.

The acceleration is positive when it is in the direction of velocity and negative when it is opposite to the direction of velocity.

Acceleration – Change in velocity

Time taken

Mathematically, a = v-u/t

SI unit of acceleration – meter/second

If an object travels in a straight line and its velocity increases or decreases by equal amounts in equal intervals of time, then the acceleration of the object is said to be uniform.

An object can travel with non-uniform acceleration if its velocity changes at a non-uniform rate.

Calculations:

Ex-1: Change in velocity of an object per unit time is called ……………

a)      Speed

b)      Motion

c)      Acceleration

d)     None

Answer: The rate of change in the velocity of an object per unit time is referred as acceleration and the kind of motion is known as accelerated motion.

Ex-2: A car is accelerates uniformly from 15 m/s to 30 m/s n 5s. What will be the acceleration of the car?

a) 1 m/s                        b) 2 m/s                       c) 3 m/s                       d) zero

u = 15 m/s

v = 30 m/s

t = 5 s

v = u + at

a = v – u/t

a = 30 -15 / 5 = 3 m/s

Ex-3: Rina swims in a 90 m long pool. She covers 180m in one minute by swimming from one end to the other and back along the same straight path. Find the average velocity of Mina.

a) Zero                        b) Infinite                    c) Constant                  d) None

Total distance traveled by Mina = 180 m/min

Displacement of Mina in 1 min = 0 m

Total time = 1 min = 60 s

Average velocity = Displacement      =  0 m   = zero

Total time taken      60 s

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