Question

The current world record for the men's 400 m sprint is a time of 43.18 seconds, set by united states athlete Michael Johnson in 1000. Calculate the average speed of this athlete in kilometres per hour. give your answer to 2 decimal places

Answer 1

k

Answer 2

They give you distance of 400 m traveled in 43.18 seconds

Answer 3

\[\frac{ 400m }{ 43.18s }\]

Answer 4

to convert these, do the following...

Answer 5

see how the initial fraction, 400m / 43.18 s is just multiplied by ratios of 1, to cancel units to the ones you are looking for , km / hr

Answer 6

1 km = 1000m
60 s = 1 min
60 min = 1 hr

all ratios of 1, and the units cancel

Answer 7

Sorry i don't quite understand the diagram, and where 10 to the power of 3 came from as well, what are the steps you made to get these figures and the final equation?

Answer 8

The diagram is just a way to represent multiplying fractions together. like
\[\frac{ x }{ y }*\frac{ t }{ s }*\frac{ v }{ u }\]

just used vertical lines as the multiply,, it makes it easier to cancel units that are in the top and bottom

Answer 9

10^3 = 1000, there are 1000 meters in 1 kilometer

Answer 10

See how the fractions are arranged, to cancel out the meter from top and bottom, and leave kilometer in the answer

Answer 11

wait so i am meant to multiply from left to right in the diagram on the top and bottom rows?

Answer 12

yeah, it is just 4 fractions multiplied together

\[\frac{ a }{ b }*\frac{ c }{ d }*\frac{ e }{ f }*\frac{ g }{ h } = \frac{ a*c*e*g }{ b*d*f*h }\]

Answer 13

I just told you about that way to do the unit conversions, cuz i think it makes it much simpler. You can decide if you need to multiply or divide much easier, because you look at the units first.

Answer 14

like turning meters to kilometers

you use the relation 1 km = 10^3 m or 1000 m and arrange the fraction to cancel the units correctly... like...

Answer 15

makes it easy to see whether to multiply by 1000 or divide by 1000, you want the m to cancel out, so put it in thebottom

Answer 16

so i divide 400/43180?

Answer 17

that is just to convert to km/s, to convert the seconds to hours, you need to do the whole thing like ...