Question

The diagram above shows the pattern of the oil dripping on the road, at a constant rate from a moving car. What information(s) do you get from it about the motion of car ?

• A. Initially it is moving with a constant speed and then it speeds up.
• B. Initially it is moving with a constant speed and then it slows down.
• C. It is moving with a constant speed.
• D. None of the above.

Answer 1

Answer: (B)

Initially it is moving with a constant speed and then it slows down.

Since oil is dropping from the car at a constant rate, distance between consecutive oil drops tells us about the speed of the car. Suppose the time interval between fall of two consecutive drops is $t$. If the distance between two consecutive drops is $d$, then speed of the car is $v=\frac{d}{t}$.
Initially, car is moving with constant speed, but later value of $d$ starts decreasing, which means car is slowing down.