Picnickers see a lightning flash and hear the resulting thunder 7.9 s later. If the storm is traveling at a rate of 20. km/h, how long, in minutes, do the picnickers have before the storm arrives at their location?

Answer 1

Well, speed of sound in air is around 343 m/s depending on pressure, humidity etc

the lightning light travels so fast we will assume we see it when it happens.

so d = 7.9 s * 343 m/s = 2710 m or 2.7 km away

t = 2.7 km /20 km/h = .135485 hours
* 60 min/hr = 8.1 minutes