Question

Benjamin watches a thunderstorm from his apartment window. He sees the flash of a lightning bolt and begins counting the seconds until he hears the clap of thunder 10. later. Assume that the speed of sound in air is 340 m/. How far away was the lightning bolt a) in m? b) in km? (Note: The speed of light, 3.0 x 108 m/*, is considerably faster than the speed of sound. That is why you see the lightning flash so much earlier than you hear the clap of thunder. In actuality, the lightning and thunder clap occur almost simultaneously.)

Answer 1

a. Given: vav 340 m/*

Δt=10.0 *

Unknown: Δd = ?

Original equation: vav =Δd /Δt

Solve: Δd = vavΔt = (340 m/)(10. ) = 3400 m

b. For numbers this large you may wish to express the final answer in km rather than in m. Because “kilo” means 1000, then 1.000 km = 1000. m.

The lightning bolt is 3.4 km away, which is just a little over two miles for those of you who think in English units!