Question

In 100 m race, A covers the distance in 36 seconds and B in 45 seconds. In this race A beats B by:
A. 20 m B. 25 m
C. 22.5 m D. 9 m

Answer 1

@e.cociuba

Answer 2

@msingh

Answer 3

@triciasotaso

Answer 4

@Prudence

Answer 5

the average speed for both runners
is
\[v_a =\frac{ 100 }{ 36 }=\frac{ 25 }{ 9 } ,v_b=\frac{ 100 }{ 45 }=\frac{ 20 }{ 9 }\]
\[v_a-v_b=\frac{ 5 }{ 9 }\]
so\[x=(v_a-v_b)t \implies \frac{ 5 }{ 9 }t\]

Answer 6

the race finish after
t=45
then
x=25

Answer 7

not sure about the logic

Answer 8

Thanks

Answer 9

the physical meaning of v_a-v_b can be considereed as the speed needed to cathc up the fastest runner

Answer 10

yw

Answer 11

Find B's velocity, then find how far he's gone after 36 seconds (this is when A crosses the line, ie he's run 100m).

Subtract that distance from 100m (eg if B has only run 75m, he's 25m behind when A finishes)

Answer 12

You need to know what distance B had travelled at the moment when A finished the 100 m. This distance cannot be found from the information given. For example B could possibly have been only 10 m behind when A crossed the finishing line and then slowed down drastically over the last 10 m.

Answer 13

Good point @kropot72 but I think it's reasonable to assume an average velocity.

Answer 14

Although, given that it took FORTY FIVE SECONDS to finish a 100m race... you might be right.

Answer 15

@agent0smith You are right, that was part of my thinking on this one :)