Question

During a school race, Sonic ran around the entire track 5 times in 10 seconds. Everyone was shocked by his speed, which was equal to 321 m/s. FINISH R D In the diagram above, D = 2R. What is the radius of the round part of the track, R, equal to? Use n = 3.14. The answer should be rounded to 3 significant figures.
63.4
62.5
61.4
60.1​

Answer 1

Step-by-step explanation:

there is no diagram here.

I assume that the race track is a rectangle in the middle and two half-circles at the left and right ends, and that the length of the rectangle is D = 2R. which makes the rectangle actually a square, as the width is the diameter of the (half-)circles, which is also 2R.

Sonic ran the track 5 times in 10 seconds with a speed of 321 m/s.

that means he ran 10×321 m in 10 seconds = 3210 m.

so, 5 times the track is 3210 m, which means that the track itself is 3210/5 = 642 m long.

and based on the assumptions above the track consists of 2 times the length of the rectangle (or square), and the full circumference of a circle with radius R (2 half-circles make one full circle).

we know the formula for the circumference of a circle :

2×pi×radius

so, we have then

642 = 2×2R + 2×pi×R = R×(4 + 2×pi)

R = 642 / (4 + 2×pi) = 62.43201701...

and when using the requested "cut-off" pi = 3.14, we get

R = 642 / (4 + 2×3.14) = 62.45136187...

and that is rounded 62.5

so, the second answer option is correct.

Answer 2

The second option is correct 62.5