Physic - Linear

Question

For a particular 100m sprint run the coaches want the race analyzed in intervals. The winner’s time was 10 seconds. She traveled the first 15 meters in 2.3 seconds, the next 70 meters in 6.5 seconds and final 15 meters in 1.2 seconds. Determine the average velocity for the entire race and for each of the 3 intervals.

Which ONE of the following statements regarding the 100m sprint is INCORRECT. 

a. The average velocity is 10 m/s.

b. She finished the last 15 meters with a faster average velocity compared to the first 15 meters.

c.  Her average velocity for the middle 70 meters was 10.77 m/s

d. She was still accelerating over the last 15 meters.

e. Her average velocity for the final 15 meters is calculated by (15 meters/ 1.2-6.5 seconds).

Answer 1

(a), (b), and (c) are all correct.

 

Item (e) is definitely wrong as written.  Her average velocity over the final 15 meters is (15 m)/(1.2 sec) = 12.5 m/sec, not (15 m)/(1.2 - 6.5 sec).  Check to see if you wrote it down correctly.

 

(d) may be wrong as well.  She averaged 10.77 m/s in the middle 70 m and 12.5 m/s over the final 15 m, so she did accelerate.  However, she may have accelerated to that speed in the final part of the 70 m, and stopped accelerating as she entered the final 15 m.  So there's not enough information to say that she was accelerating over the final 15 m.