Question

An athlete completes one round of a circular track of radius R in 40 seconds.What will be his displacement at the end of 2 min and 20sec?

Answer 1

so here is what I did,
since in 40 sec, it travelled 2(pi)R,
so in 140 sec, it moved 7(pi) R,
but this is wrong?

Answer 2

the answer I have is 2R? how?

Answer 3

Yes I think so it should be 2R.

Answer 4

how?

Answer 5

\[(pi \times R ^{2})\div(140)\]

Answer 6

Excuse me, \[(pi \times R^{2}) \div (140/40)\]

Answer 7

First find velocity from the given data. use the equation\[\Large v=\frac{s}{t}\]

Answer 8

\[\Large s=2pir\]
t=40s

Answer 9

yes. substitute your velocity in again that formula for 2min and 40sec calculation.

Answer 10

so 2piR/40 x 140= 7 pi R

Answer 11

??? how? wrong. 7piR. ??
it must be 2piR

Answer 12

circ = 2piR you're right
so,

2piR(140/40)

I always get circ and area mixed up

Answer 13

does this calculation giving you 7piR??

Answer 14

yeah

Answer 15

circ = 2piR you're right
so,

2piR(140/40)

I always get circ and area mixed up

Answer 16

circ = 2piR you're right
so,

2piR(140/40)

I always get circ and area mixed up

Answer 17

so is the answer 7 pi R? or 2R?

Answer 18

my calculations are giving me 2piR

Answer 19

2piR/40 x 140
this was your equation?

Answer 20

\[v=\frac{s}{t}\]\[v=\frac{2piR}{40}\]\[v=\frac{piR}{20}\]Now use this \[s=v*t\]\[s=\frac{piR}{\cancel{20}}*\cancel{40}2\]\[s=2piR\]This is how I am trying to do this dear.

Answer 21

since velocity is the same so shouldn't we put 140 sec instead of 40 sec in the s=vxt equation?

Answer 22

2piR(140/40)=7piR

If you take off all but the fraction of the last lap, you get:

piR
voila

Answer 23

displacement = piR

Answer 24

oh... it is 2min and 20 sec. why i thought it is 80 sec. yes you will put 140s

Answer 25

displacement = piR

where 40s is the time for 1 lap,
140s is the time of full run
R = radius of circular lap

Answer 26

displacement = piR. how? not halfway track. it is full track though.. isn't it?

Answer 27

DISPLACEMENT = distance from START

Answer 28

the displacemen for half is + and for next half it is -. you mean this? inclusive directions?

Answer 29

140s/40s = 3.5 laps
.5 = displacement
.5*2piR = piR

Answer 30

@physicsme are you getting this point?

Answer 31

I think you might be confusing Displacement with total distance...@physicsme

Answer 32

Turning test making abuses.

Answer 33

gimme a medal or something, guys

Answer 34

yeah, I got it, hit me right after the computer shut down, @Dyiliq you're right, i was mixing displacement with distance.
thanks @Shayaan_Mustafa and @Dyiliq :)