Question

What is average velocity? If a driver decreases the speed of a car from $25 ms^{-1}$ to $10 ms^{-1}$ in $5$ seconds? Find out the acceleration of the car.

Answer 1

Hint: Velocity is the speed at which an object travels. It holds both a magnitude and a direction. When velocity variations due to constant acceleration, the average velocity can be obtained by adding the initial and final velocities and distributing by $2$. The velocity unit is meters per second. This formula fits constant acceleration only. Acceleration is the pace of change of velocity with the period. The word acceleration is usually used to define a state of raising speed.

Complete step by step solution:
The average velocity of a body is its total displacement shared by the whole time taken. In another word, it is the pace at which an object displaces its position from one position to another. Average velocity is a vector term.
Given: The speed of a car decreases from $25 ms^{-1}$ to $10 ms^{-1}$ in $5$ seconds.
Initial velocity, $u = 25 ms^{-1}$
Final velocity, $v = 10 ms^{-1}$
Time taken, $t = 5$ seconds
We will use the first equation of motion to find out the acceleration of the car.
$v = u + at$
Where, v is final velocity.
u is the initial velocity.
t is time taken.
Put all values in the above equation.
$10 = 25 + a \times 5$
 $\implies 5a = -15$
It gives,
$a = -3 ms^{-2}$
The acceleration of the car is $-3 ms^{-2}$.

Note: Average speed is described as the total distance covered by the time taken, whereas average velocity is described as the displacement by the time received. Since speed is a scalar term, the average speed is also a scalar quantity, while velocity is a vector term. Hence, the average velocity is a vector term.