Chapter 1, Problem 9CA

To determine

To choose: The expression that do not represent the average speed of the car from the options.

Answer to Problem 9CA

The expression $\text{80}\frac{\text{seconds}}{\text{feet}}\text{ and }\frac{\text{second}}{\text{80feet}}$ do not represent the average speed of the car.

Explanation of Solution

Given:

The distance is $1000$ feet and time is $12.5$ seconds.

Formula Used:

The formula of the average speed of an object is represented below.

$\text{Average speed}=\frac{s}{t}$ ....... (1)

Here, $s$ denotes the distance and $t$ denotes the time.

Substitute the value $s=1000\text{feet}$ and $t=12.5\sec$ in equation (1) to obtain the value of average speed of a car.

$\begin{array}{c}\text{average speed}=\frac{1000\text{ feet}}{12.5\text{ seconds}}\\ =\frac{10000\text{ feet}}{125\text{ seconds}}\\ =\frac{400\text{ feet}}{\text{5 seconds}}\\ =\frac{\text{80 feet}}{\text{ seconds}}\text{ or 80}\frac{\text{ feet}}{\text{ seconds}}\end{array}$

The expression of average speed of a car can be expressed as follows:

$\frac{\text{80 feet}}{\text{ seconds}}\text{ or 80}\frac{\text{ feet}}{\text{ seconds}}$

Therefore, the expression $\text{80}\frac{\text{seconds}}{\text{feet}}\text{ and }\frac{\text{second}}{\text{80feet}}$ do not represent the average speed of the car.

Conclusion:

Thus, the expression $\text{80}\frac{\text{seconds}}{\text{feet}}\text{ and }\frac{\text{second}}{\text{80feet}}$ do not represent the average speed of the car.