Question

A ball is hung by a string from the ceiling of a car moving on a straight and smooth road. If the string is inclined towards the front side of the car making a small constant angle with the vertical, then the car is moving with
A. Constant velocity
B. Constant acceleration
C. Constant retardation
D. Increasing acceleration
E. Decreasing acceleration

Answer 1

Hint: The change in the velocity which may increase or decrease with respect to time is known as the acceleration. The retardation is the act of slowness or the delay. It is the negative acceleration. Here, we will visualize and will draw with the help of the ray diagram the exact scenario and will decide accordingly the motion of the car.

Complete step by step answer:
As, shown in the above figure,
We can get-
\[
  \tan \theta = \dfrac{{ma}}{{mg}} \\
   \Rightarrow \tan \theta = \dfrac{a}{g} \\
 \]
Since, the angle is negative. It gives us a negative acceleration.
And negative acceleration is known as the retardation.

So, the correct answer is “Option C”.

Note:
To solve these types of word problems, know the difference between the terms. Constant velocity is the fixed velocity when an object travels an equal distance in equal interval of time throughout its journey. Constant acceleration is the velocity of the particle which changes at a constant rate. Increase in acceleration is the increase in acceleration proportionally with respect to the force.