9. Question : Cheryl runs a race on a circular 400.0 m track. She starts running east at the starting line and stops 20.0 m west of the starting line. Her time is 8.0 × 101 s. What is her average speed?

4.8 m/s

2.1 × 10-1 m/s

-2.5 × 10-1 m/s

5.0 × 101 m/s

what is the right one?

To find Cheryl's average speed, we can use the formula:

average speed = total distance / total time

In this case, Cheryl runs a circular track. The total distance she ran is equal to the circumference of the track, which is 400.0 m. However, since she ends up 20.0 m west of the starting line, we need to subtract this distance from the total distance she ran.

So the total distance Cheryl ran is 400.0 m - 20.0 m = 380.0 m.

Her time is given as 8.0 × 10^1 s.

Now we can plug these values into the formula:

average speed = 380.0 m / 8.0 × 10^1 s

Simplifying the expression:

average speed = 4.75 m/s

Therefore, Cheryl's average speed is 4.75 m/s.

To find Cheryl's average speed, we need to calculate the total distance covered, and then divide it by the total time taken.

In this case, Cheryl runs on a circular track, starting east and ending 20.0 m west of the starting line. This means she has covered the entire circumference of the track, which is 400.0 m.

Next, we calculate the total distance covered. Since Cheryl starts and stops at the same point, we need to consider her entire journey around the track. So the total distance covered is the circumference of the track (400.0 m).

Finally, we divide the total distance covered (400.0 m) by the total time taken (8.0 × 10^1 s) to find Cheryl's average speed.

Using the equation: Average Speed = Total Distance / Total Time

Average Speed = 400.0 m / (8.0 × 10^1 s)

Simplifying the equation, we get:

Average Speed = 5.0 × 10^1 m/s

Therefore, the correct answer is 5.0 × 10^1 m/s.