According to the rule of thumb, every five seconds between a lightning flash and the following thunder gives the distance to the flash in miles.
(a) Assuming that the flash of light arrives in essentially no time at all, estimate the speed of the sound in m/s from this rule.
(b) What would be the rule for kilometers?
(a) The estimated value of the speed of the sound is .
(b) The rule for kilometers will be ‘every three seconds between a lightning flash and the following thunder gives the distance to the flash in kilometers.’
There is a gap of five seconds between the lightning flash and the following thunder that gives the distance to the flash in miles.
So, the sound is traveling one mile in 5 seconds.
You know that .
Here, the distance traveled by the sound is 1 mile.
Therefore, the estimated speed of the sound is .
(b) Let the sound take time to travel a distance of 1 km or 1000 m.
Therefore, the rule is ‘every three seconds between a lightning flash and the following thunder gives the distance to the flash in kilometers.’
Agent Bond is standing on a bridge, 15 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this region. The roof of the truck is 3.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he drops down from the bridge onto the truck, making his getaway. How many poles is it?
Suppose you adjust your garden hose nozzle for a fast stream of water. You point the nozzle vertically upward at the height of 1.8 m above the ground (Fig. 2–40). When you quickly turn off the nozzle, you hear the water striking the ground next to you for another 2.5 s. What is the water speed as it leaves the nozzle?
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