At 7:14 A.M. on June 30, 1908, a huge explosion occurred above remote central Si

Question

At 7:14 A.M. on June 30, 1908, a huge explosion occurred above remote central Siberia at latitude 61° N and longitude 102° E; the fireball thus created was the brightest flash seen by anyone before the advent of nuclear weapons. The Tunguska Event, which according to one change witness “covered an enormous part of the sky,” was probably the explosion of a stony asteroid about 140 m wide.


(a) Considering only the Earth’s rotation, determine how much later the asteroid would have had to arrive to put the explosion above Helsinki at longitude 25° E? This would have obliterated the city.


(b) If the asteroid had, instead, been a metallic asteroid, it
could have reached the Earth’s surface. How much later would such an asteroid have had to arrive to put the impact in the Atlantic Ocean at longitude 20° W? (The resulting tsunamis would have wiped out coastal civilization on both sides of the Atlantic.)

Explanation / Answer

The only thing you have to know in this problem is that the earth rotates longitudally at 360 degrees/day clockwise when looking down at the north pole.

For the asteroid to impact at 25 degrees E, the earth would need to rotate an extra 77 degrees. If the earth rotates 360 degrees in 24 h, it rotates 77 degrees in 5.1 h.

Similarly, for the asteroid to impact at 20 degrees W, the earth would need to rotate an extra 122 degrees. It takes 8.1 h for the earth to rotate 122 degrees.

I hope this helps.

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