Question

A car is starting from rest. After traveling 100m the car comes to rest. What is the car's average velocity?
(A) $0{\text{ km/h}}$
(B) $48{\text{ km/h}}$
(C) $50{\text{ km/h}}$
(D) $60{\text{ km/h}}$
(E) $100{\text{ km/h}}$

Answer 1

Hint Use the average velocity formula to find the car’s average velocity. In the question provided the car is not in a motion. The car is in the same position, so the total displacement and velocity of the car is zero.
$\Rightarrow {\text{Average velocity = }}\dfrac{{{\text{Initial velocity + Final velocity}}}}{2}$

Complete step by step answer
Given, The displacement is $0{\text{ m}}$
The initial velocity of the car is $0{\text{ m/s}}$
Final velocity of the car is $0{\text{ m/s}}$
Velocity: The velocity of an object is defined as the change of rate of its position with respect to time and direction. The unit of velocity is ${\text{m/s}}{\text{.}}$ Velocity is a vector quantity.
Velocity = Displacement/Time taken.
The velocity at which the object starts moving is known as initial velocity and the velocity at which the object stops moving is known as final velocity.
Here, the displacement is the distance travelled by the object. It is calculated by subtracting the initial distance travelled from the final distance travelled by the object. It is a vector quantity. Its unit is metre.
Displacement = Final distance travelled – Initial distance travelled
Average velocity: It is defined as the sum of initial velocity and final velocity divided by 2.
$\Rightarrow {\text{Average velocity = }}\dfrac{{{\text{Initial velocity + Final velocity}}}}{2}$
Substitute the given values we get,
$\Rightarrow {\text{Average velocity = }}\dfrac{{{\text{0 + 0}}}}{2}$
$\Rightarrow {\text{Average velocity = 0}}$
Hence the correct answer is option (A) $0{\text{ km/h}}$.

Note
Velocity and displacement are different from speed and distance. Even though they seem similar, velocity and displacement is vector quantity i.e. they are directional in nature. But speed and distance are scalar quantities; they are not directional. In other words velocity is speed with direction and displacement is distance travelled in a particular direction.