Question

A car is moving with a uniform velocity of $40km{h^{ - 1}}$ in a straight line. Its acceleration after $1hour$ is:

Answer 1

By definition, Acceleration is the rate of change of velocity per unit of time. Hence when we want to calculate the acceleration of an object during its motion, we divide the amount of change in velocity in a certain time by the time.
Note that, according to Newton’s $1^{st}$ law of motion when an object moves in a straight line without changing its velocity that means with a uniform velocity this implies that no force is applied to it. And, from the second law of motion, we also get the relation between force and acceleration.
The whole concept is essential to calculate the acceleration required in the question.

Formula used:
Acceleration $a = \dfrac{{{v_f} - {v_i}}}{t}$
${v_f} - {v_i} =$ amount of change in velocity during the time $t$.

Complete step by step solution:
It is given that, A car is moving with a uniform velocity of $40km{h^{ - 1}}$ in a straight line.
Acceleration is the rate of change of velocity per unit time. So, to calculate the acceleration of the car during its motion the amount of change in velocity in the given time $t$ is needed.
The amount of change in velocity during the time $t$ is ${v_f} - {v_i} = 40 - 40 = 0$
So, the Acceleration $a = \dfrac{{{v_f} - {v_i}}}{t} = 0$
Hence, the acceleration after $1hour$ is $0 m/s^2$

Note:
We can find the acceleration also by the concept that, According to Newton’s $1st$ law of motion when an object moves in a straight line without changing its velocity, no force is acting on it. Or we can say since there is no force applied to the object; the object is moving in a straight line with a uniform velocity.
From Newton’s $2^{nd}$ law of motion, we get that the relation between the applied force and acceleration is, $F = ma$
Hence if the force $F = 0$, then the acceleration also becomes zero.