Chapter 2, Problem 1OQ

One drop of oil falls straight down onto the road from the engine of a moving car every 5 s. Figure OQ2.1 shows the pattern of the drops left behind on the pavement. What is the average speed of the car over this section of its motion? (a) 20 m/s (b) 24 m/s (c) 30 m/s (d) 100 m/s (e) 120 m/s

Figure OQ2.1

To determine

The average speed of the car over the given section of motion.

Answer to Problem 1OQ

Option (b).

Explanation of Solution

Write the equation for the average speed.

  $v_{\text{avg}}=\frac{\text{Total distance}}{\text{Total time}}$        (I)

Here, $v_{\text{avg}}$ is the average speed.

Since there are five time intervals during the given section of motion and each time interval is $5\text{ s}$, the total time will be equal to $5\times 5\text{ s}=25\text{ s}$.

Substitute $600\text{ m}$ for total distance and $25\text{ s}$ for total time in equation (I) to find $v_{\text{avg}}$.

  $\begin{array}{c}{v}_{\text{avg}}=\frac{600\text{ m}}{25\text{ s}}\\ =24\text{ m/s}\end{array}$

Conclusion:

Since the average speed of the car during the given section of motion is $24\text{ m/s}$, option (b) is correct.

Since the average speed of the car during the given section of motion is not $20\text{ m/s}$, option (a) is incorrect.

Since the average speed of the car during the given section of motion is not $30\text{ m/s}$, option (c) is incorrect.

Since the average speed of the car during the given section of motion is not $100\text{ m/s}$, option (d) is incorrect.

Since the average speed of the car during the given section of motion is not $120\text{ m/s}$, option (e) is incorrect.