In: Physics
Let's calculate how long it takes each of them to run the
wholerace.
Renee: She must travel 20 m to the end of the track and then 20
mback, so a total of 40 m. She runs 2.0 m/s. Distance = speed
*time, so time = distance/speed. Thus, her time is 40/2.0 =
20seconds.
Phillippe: When Phillippe is running in the same direction as
thesidewalk is moving, his velocity relative to the sidewalk is
addedto the velocity of the sidewalk for a total velocity of 2.0 +
1.5 =3.5 m/s relative to the ground. He runs 20 m at this pace, so
ittakes him 20/3.5 = 5.7 sec. On the way back, the sidewalk is
movingin the opposite direction, so his speed relative to the
ground is2.0 - 1.5 = 0.5 m/s. Thus, the time it takes him to run
back is20/.5 = 40 sec. So his total time is 40 + 5.7 = 45.7
seconds.
Clearly, Renee wins therace. She wins by a total
of 45.7 - 20 = 25.7 seconds. In 2 sigfigs, this is
26seconds.
Edit: Also, I don't know what the etiquette about this is, but
theperson who posted below me has absolutely no idea what
they'retalking about. They misunderstood the question and also
didn't evenget the correct answer for the misinterpreted
question...