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Physics problems

D

Dritnul

Senior member
ok so to summarize it some1 is listening to the radio broadcast of a baseball game 1.6Km south of the baseball game.
she hears the EMP from lightning over the radio
2 secs later she hears thunder over the baseball stadium mic
4 secs later thunder hits her house

where is lightning with respect to baseball field?
 
wouldnt it be 6seconds*speed of sound away? in which case, its 2400m away (4 seconds to get to her house, 1600m away)

edit: w/ respect to baseball field, only 800m
 
Not completely solvable (there are 2 possible solutions).

660 metres either due 127 or 233 from the stadium.
 
Originally posted by: Fenixgoon
wouldnt it be 6seconds*speed of sound away? in which case, its 2400m away (4 seconds to get to her house, 1600m away)

edit: w/ respect to baseball field, only 800m
Click to expand...

it takes 4 secs total to get to her house
 
Originally posted by: Mark R
Not completely solvable (there are 2 possible solutions).

660 metres either due 127 or 233 from the stadium.
Click to expand...

How'd you come up with that? it sounds right....but i dunno
 
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
 
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...

they can't be in a straight line? 😀
 
Originally posted by: Fenixgoon
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...

they can't be in a straight line? 😀
Click to expand...

no because if it were in between them in a straight line the park and house would have to be ~2Km away
 
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...


That seems to imply that the storm cloud is at ground level, which it's not. You need to take altitude into account.

So now that there's altitude to deal with, there are many more than 2 solutions. You wouldn't have just left/right to contend with, you'd have a points in between at various altitudes.
 
Originally posted by: 91TTZ
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...


That seems to imply that the storm cloud is at ground level, which it's not. You need to take altitude into account.

So now that there's altitude to deal with, there are many more than 2 solutions. You wouldn't have just left/right to contend with, you'd have a points in between at various altitudes.
Click to expand...

however no altitude is given so its kinda hard to assume an altitude w/o at least a cloud type

besides its only university physics so its still slightly simplified physics
 
Originally posted by: Dritnul
Originally posted by: 91TTZ
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...


That seems to imply that the storm cloud is at ground level, which it's not. You need to take altitude into account.

So now that there's altitude to deal with, there are many more than 2 solutions. You wouldn't have just left/right to contend with, you'd have a points in between at various altitudes.
Click to expand...

however no altitude is given so its kinda hard to assume an altitude w/o at least a cloud type

besides its only university physics so its still slightly simplified physics
Click to expand...


But if they're trying to find an answer to this problem, how can they ignore very basic factors which affect the result? They want an answer but are assuming that a cloud has no altitude? Why even give an answer if it's most likely wrong?

 
Originally posted by: Dritnul
ok so to summarize it some1 is listening to the radio broadcast of a baseball game 1.6Km south of the baseball game.
she hears the EMP from lightning over the radio
2 secs later she hears thunder over the baseball stadium mic
4 secs later thunder hits her house

where is lightning with respect to baseball field?
Click to expand...

Unless the baseball game has its own radio tower for broadcasting (it shouldn't), hearing the EMP from lightning doesn't help you at all.

One can't know the speed of sound without knowledge of several factors, temperature being the most important. Thus, hearing the thunder is also useless unless you also know the temperature. The fact that there's lightning is in no way relevant to determining the temperature of the region.

Done, the solution can't be found without more information. I'm assuming you'd want to be precise, as the sound of thunder in southern Arizona would be significantly faster than the sound of thunder in northern Canada.
 
Originally posted by: 91TTZ
Originally posted by: Dritnul
Originally posted by: 91TTZ
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...


That seems to imply that the storm cloud is at ground level, which it's not. You need to take altitude into account.

So now that there's altitude to deal with, there are many more than 2 solutions. You wouldn't have just left/right to contend with, you'd have a points in between at various altitudes.
Click to expand...

however no altitude is given so its kinda hard to assume an altitude w/o at least a cloud type

besides its only university physics so its still slightly simplified physics
Click to expand...


But if they're trying to find an answer to this problem, how can they ignore very basic factors which affect the result? They want an answer but are assuming that a cloud has no altitude? Why even give an answer if it's most likely wrong?
Click to expand...

Because technically there are an infinite number of xyz coordinates for the cloud. The answer specifically asks for "where does the lightning strike?" The cloud doesn't generate the sound. You're hearing ionized air, so the noise comes from all along the lightning strike. Due to the speed of sound being approximately constant and due to obvious geometric reasons, you'll hear the lightning as it strikes the ground before you'll hear the lightning coming from the cloud.

In other words, all of the information assumes you hear the thunder originating from the ground. This only makes sense, the beginning of the thunder (the beginning of the rumbling) corresponds to the point on the ground where the lightning bolt struck.
 
Originally posted by: Eeezee
Originally posted by: 91TTZ
Originally posted by: Dritnul
Originally posted by: 91TTZ
Originally posted by: Mark R
Treat the home, stadium and storm as the three points of a triangle. You know the lengths (either given in the question, or from the time delay).

Then use cosine rule to find the angle. Due to symmetry there are 2 solutions.
Click to expand...


That seems to imply that the storm cloud is at ground level, which it's not. You need to take altitude into account.

So now that there's altitude to deal with, there are many more than 2 solutions. You wouldn't have just left/right to contend with, you'd have a points in between at various altitudes.
Click to expand...

however no altitude is given so its kinda hard to assume an altitude w/o at least a cloud type

besides its only university physics so its still slightly simplified physics
Click to expand...


But if they're trying to find an answer to this problem, how can they ignore very basic factors which affect the result? They want an answer but are assuming that a cloud has no altitude? Why even give an answer if it's most likely wrong?
Click to expand...

Because technically there are an infinite number of xyz coordinates for the cloud. The answer specifically asks for "where does the lightning strike?" The cloud doesn't generate the sound. You're hearing ionized air, so the noise comes from all along the lightning strike. Due to the speed of sound being approximately constant and due to obvious geometric reasons, you'll hear the lightning as it strikes the ground before you'll hear the lightning coming from the cloud.

In other words, all of the information assumes you hear the thunder originating from the ground. This only makes sense, the beginning of the thunder (the beginning of the rumbling) corresponds to the point on the ground where the lightning bolt struck.
Click to expand...

But since you're trying to find out where the sound is coming from in relation to the house and the stadium, you can't really tell from the info provided. I'm sure they're looking for an answer along the lines of "if you hear the zap over the radio at 4:00:00, the thunder takes 2 second to get to the stadium and 4 seconds after that to get to the house, then the cloud is here at x,y" I'm sure they want that, but you can't really figure that out.

For one, not all lightning reaches the ground. In fact, most doesn't. That cloud could be 2 miles up. You can't really tell how far between the house and the stadium (ground wise) the cloud is, since we're not dealing with a 2 dimensional space.

For instance, sound travels at 340 meters/second on an average day. Let's say the house is 680 meters due south of the stadium. Let's say the sound reaches the stadium and the house at the same time, 2 seconds. You'd figure that the cloud has to be 680 meters from both the house and the stadium, meaning it's off to the left or right side of both the stadium and house.

But in reality, that doesn't have to be the case. The cloud could be directly in between. You might think that since it's in between, and the house and stadium are only 680 meters apart, that the sound would only take 1 second to get to each. But that's where altitude comes into play. The thunder could still be originating 680 meters from both the house and the stadium, it's just up in the air.
 
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