Night Photography - Street Light Question?

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Night Photography - Street Light Question? 1

1. A street light is at the top of a 18 ft tall pole. A woman 6 ft tall walks away from the pole with a speed of?

Suppose the woman is distance 2x from the foot of the lamp post. This means the tip of the shadow is 3x away from the foot of the light. (Draw a diagram and you will see - use similar triangles). So the speed of the woman is d(2x)/dt = 2dx/dt = 8 feet/sec so that dx/dt = 4 feet/sec The speed of the shadow is d(3x)/dt = 3dx/dt = 3 x 4 = 12 feet per second. It would seem that the distance from the light is not needed - unless I have made an error. Hope not.

2. how do you find the shadow of a 5 ft tall person if he or she is 30 ft away from a 20 foot tall street light?

hmmm... if theyre both congruent triangles, you should be able to compare them, right? so i would say 20 is to 30 as 5 is to x. which comes out to 7.5. did i do something wrong? what am i missing?

Night Photography - Street Light Question? 2

3. A street light is at the top of a 11 ft tall pole. A woman 6 ft?

| |5. |___ |..x..| |....6|... |......|..... |___.|____ ...x.....s draw diagram like the one above and let x be the distance of woman from pole and let s be the length of shadow. The two little triangles are similar so their gradients are equal 5/x = 6/s so s = (6/5)x differentiate both sides with respect to time gives ds/st = (6/5)dx/dt and your given dx/dt = 5ft/s so ds/dt=6ft/s is the speed of the shadow it's constant and does not depend on x so the 35ft is useless (note: the above answer mistakenly found the velocity of woman plus shadow 56=11) 2. Here it's best to just think of one of them moving rather than both ie consider the situation from A's perspective, A is stationary at the origin of your graph and sees B at x=50mi east of him travelling east (x) at dx/dt=17mi/hr and north (y) at dy/dt=25mi/hr so the position of B relative to A, by integration if you like, as a function of time is x = 5017t y = 25t the distance between them is D = (x y) = ((5017t) (25t)) = plug in t=5 is the answer 3. given dV/dt = 20ft^3/min and r/h = constant = k say so r = kh substitute in V = (1/3)pi r^2h = (1/3)pi k^2h^3 DV/dt = pi k^2h^2dh/dt need to know the k = r/h ratio to solve this one ,.,.,.,

4. A street light is mounted at the top of a 15 foot tall pole. A man 6 ft tall walks away from the pole with a s?

We are given the height of the pole (15 ft), the height of the man (6 ft), and the distance between them in terms of t (x=6t). How fast the tip of the shadow moving is the rate of change (over time, t) in the distance from the pole to the tip. Let D(t)=distance from the pole to the tip. D(t) = x y so D(t) = 6t y Now we know x in terms of t but we still need to get y in terms of t. We can do this by getting y in terms of x. You can see by drawing the information you are given in a diagram as I have, that x and y are related. In the diagram you should see two triangles. The dimensions of the two triangles are related as follows: 15/D = 6/y and D = x y so 15/(xy) = 6/y solve for y in terms of x y=(2/3)x so we can rewrite D=xy in terms of x only D(t)=x(2/3)x =(5/3)x we are given x=6t so D(t)= (5/3)(6t) = 10t Now that we have the distance in terms of t we can find the rate of change in the distance by taking the derivative of D(t) D'(t)=10 In some cases where the rate changes over time, you would need to plug your distance (40 ft) into D(t) as D(t), solve for t, and then plug t into D'(t), however in this case D'(t) is a constant 10 ft/s.

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Who Invented the Street Light?
someone retarded1. which china led street light manufacturer is better?My english is poor and can not tell you too much about street light products, but I suggest you see products here WWW.IBTSLED.COM2. why does the street light in front of my house keep turning on and off every few minutes?Its the ballast. When the bulbs go out they just quit working. When the ballast starts to go bad, they heat up, shut down when it cools down again they come back on till they heat up again3. Street light goes out when I walk by?please dear, do not you call yourself 'crazy' ever, please. i do not know anything useful information to help you but i do know somethings; 1st of all whoever made fun of your question is himself/herself a jerk and i knew it & so many other people know it too that when they read your question they thought of the " power" of your's & maybe a lot of them wanted/wished that what if they had the power that you have. once i watched a show on t.v. ( not faking) that on peiple with some mysterious things/power or events. on 1 particular episode, there was a man, whenever he saws a bulb or like he went into a shop & if there's a bulb it just went off without any reason like, its just fused( suddenly & it happens every-time) and did not light again( he told that himself & demonstrated it also; he said why it happenes i do not know & that's why in my home i do not have any bulbs for lighting purpose.) so i think maybe you can find some similarities inyour & his case if you believe. otherwise i just wanna say that just believe in yourself & in the good things in yourself ( by good things i did not mean that your gift is a bad thing). do take some time from your daily schedule & do some research, it will help you to find the qualities in yourself because knowing oneself, one's mind, heart & soul is like knowing or get fascinated by a superstar ( if you can like a celebraty & his life how come you do not like your's? hope you will get it what i wanna say, right na?). who knows you would be among some very lucky people who help me & other normal people like me through their gift. thanks for reading my message to you and if you like you can share anything with me. take care.4. When you were a kid did you often break the street light rule?My Dad was a Sergeant in the Army during WW 2. Have you ever heard one of those guys yell? We made it home as soon as the lights came on. Having the entire town know you were late just was not a pleasant event.. we would hear all about it at school the following day.. Sigh.5. When you were a kid did you often break the street light rule?sometimes i stay at my friends house till like 3A.M. im 14 so yea, but one time i broke a streetlight, i shot it with my bebe gun6. what does it mean when you drive under a street light and it goes out?I had a physics teacher in High School who let us ask him random questions at the beginning of class each day. One of the students asked him this question, and his answer was that each of us emit a certain energy. If the light turns off or on, it was because your energy was at the same frequency as the electricity in the bulb. He also dedicated a day of class to ESP, and got mad at us when we threw off his vibe... and he thinks JFK was abducted by aliens, and will return in the year 2025... so, you can judge yourself whether or not to give his explanation any merit... :D7. PSE Begins Smart Street Light Installations To Help Customers Save Energy, Reduce CarbonPuget Sound Energy will begin installing street light control capabilities, also known as smart street lights, to help its lighting customers save money and reduce carbon. The technology will give PSE municipal customers more choice on how they light up their roads and communities by measuring energy consumption and using adaptive controls to lower usage in specific locations and times of day while also enhancing safety measures. The smart grid technology will add controls and software to LED street lights to enable two way communication. Smart street lights can be instantly turned on and off or dimmed for benefits like energy conservation or reducing light pollution at night. The ability to monitor each light's performance means broken and failing lights can be quickly identified and repaired. Because smart street lights can operate more efficiently, customers will be able to optimize their energy use, lower costs and reduce carbon in our environment. "Our lighting customers told us they wanted more control over their energy usage to save money and reduce carbon, and this technology will help meet both those needs," said PSE Director of Product Development and Growth Will Einstein. "New technology such as smart street lights will help us partner with our customers to meet their goals and improve the customer experience." Energy measurement that would facilitate metered billing as opposed to flat rate billing Remote control for dimming, turn off and turn on Uses less energy through dimming and reduces carbon as a result The City of Bellevue will be one of the first to receive the installations. PSE will be replacing around 300 roadway lights in some of Bellevue's arterial roadways with LED lights. It's part of the city's overall effort to reduce its carbon footprint. "We value innovation as a community and so appreciate that PSE partnered with Bellevue as one of the first two cities to receive new smart street lights," said Mayor Lynne Robinson. "In addition to energy efficiency and cost savings, it has the potential to help PSE respond more quickly to burned out lights owned by the company. It will be a positive safety boost for our Vision Zero effort to eliminate serious-injury and fatal crashes on city streets by 2030." Smart street lighting installations will also soon begin in the City of Edgewood with the installation of about 50 smart light controllers. "The City of Edgewood is excited to partner with PSE to incorporate Smart technology for immediate two-way communications and control of our street lights," said Edgewood Mayor Daryl Eidinger. "This control will give us feedback for malfunctions and allow us to reduce our usage, light pollution and our carbon footprint." Other cities within PSE's service area will also be able to engage with PSE on controls. PSE has partnered with Landis Gyr to equip 25,000 street lights with smart controls over five years. This is another way PSE is working together with customers to create a clean energy future for all as the company has also set an aspirational goal to be a Beyond Net Zero Carbon company by 2045. PSE will target reducing its own carbon emissions to net zero and go beyond by helping other sectors to enable carbon reduction across the state. Partnering with municipalities in its service area will help towards that mission. For more information on the smart street lighting program.
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