Question

Which of the following is an example of uniform motion:
A) An aircraft moving through the clouds and landing
B) A car coming to a halt.
C) A car colliding with another car.
D) An aircraft cruising at a level height and a steady speed.

Answer 1

The motion of a body is said to be uniform if its speed remains constant with change in time. We can also say that acceleration in the case of uniform motion remains zero. So, if there is acceleration or deceleration in the body, we cannot say that the body is in uniform motion.

Complete solution:
We know that, for a uniform motion to occur, the body must travel equal distances in equal intervals of time.
In option (D) as the aircraft moves with a steady speed, the acceleration is zero, and thus, we can say, the aircraft moves at a uniform speed.
So, option (D), an aircraft cruising at a level height and a steady is correct.

Additional Information:
There is another kind of motion, which is the non-uniform motion. In this case, the body either increases or decreases its speed over time. In the other scenarios, we can see, when, the car comes to a halt, even its speed decreases with time and gradually becomes zero as it comes to a halt. Thus, this is also an example of non-uniform motion. Similarly, when a car collides with another car, there also occurs a change in the speed of both the cars, thus, this is also another example of non-uniform motion. Again when an aircraft is moving through the clouds and landing, its speed must decrease with time and gradually becomes zero. That is why, it is an example of decelerated motion, and hence, non-uniform motion.

Note: We know, in the case of uniform motion, the distance-time graph is always a straight line. There are mainly two kinds of motion, either uniform or non-uniform. If the motion is non-uniform, it is either accelerated, that is its speed increases with respect to time, or decelerated, that is its speed decreases with time.