A Simple ##d= vt## question, but I am confused

[billllib]

Homework Statement

Answer the following questions involving the speed of light. (Assume that the speed of light is 300,000,000 meters/second. Also ignore any relativistic effects on time and length, because we have not covered those yet. In other words, the calculations below are intended to be straightforward time and distance calculations.)

(a) The circumference of the Earth at the equator is 40,075 km. If you could travel at the speed of light, how many times could you go around the Earth in one second?

Relevant Equations

$d = vt$

I think the answer should be$c = (300,000,000 ~meters/second)$

$300,000 km = \frac {300,000,000 ~ \rm{m/s}} {1000 ~\rm{km}}$

$d = vt$

$d = 40,075 km$

$t = \frac d v$$40075 km / 300 000 km/s =0.1336 s$

Why is the answer 7.5?
An help appreciated

 

[fresh_42]

If you can go 300,000 km in one second, how many times can you go 40,075 km in a second?

If a wall is seven meters long and your scale is two meters long, how many of them can you lay along the wall?

 

[billllib]

Got it just misread the question thanks.

 

[scottdave]

$300,000 km = \frac {300,000,000 ~ \rm{m/s}} {1000 ~\rm{km}}$

One thing I noticed with your formula, above: To keep the units and dimensions correct, it should actually be this:

$300,000 ~ \rm{km/s} = \frac {300,000,000 ~ \rm{m/s}} {1000 ~\rm{m/km}}$

I'll take this moment to plug my Insights article - https://www.physicsforums.com/insights/make-units-work/
I hope you enjoy it.

 

[billllib]

Thanks