On the first. I absolutely do not understand how you got f=48mm
M=hi/ho=1.8/.008 figure ti.
M=do/di and you know do, so figure di
then use the lens equation to solve for f.
On the second.
cost/joule=12/joules=12/calories*4.2
-Using a digital camera, you are taking a picture of your 1.80meter-tall friend standing at a distance of one meter from you. From the camera manual, you learned that the size of the sensor (electronic film) is 6mmx8mm. In other words, the sensor is rectangular with 6mm on one side and 8mm on the other. Calculate the focal length of the camera zoom lens that is required to fit the whole image of your friend onto the sensor.
Okay, here is what i got:
using the lens makers eq
(1/p)+(1/q)=(1/f)
so, f=6x8=48mm
(1/1000mm)+(1/q)=(1/48mm)
then,
q=50.42 so,
m=(q/p)= (50.42/1000)=0.0504
1.8meters=1800mm so,
1800mm x 0.0504=90.72mm
*Can someone check my calculation for this problem?*
-An average person needs 2,000 Kcal of energy a day. One Kcal = 1,000 calories and one calorie = 4.184 Joules.
-----Estimate the cost of foods that you take each day and calculate the cost for you to produce one Joule of energy, excluding health maintenance and clothing costs. This is referred to as direct human energy cost, excluding overhead charges.
*Okay so i figured that it takes 8368000 joules a day from the given info but how do i figure cost of one joule? i figure i use about $12 a day on food.
Last prob that i need help on:
Find out the baseline cost of electricity per KWxHour at home, where KW = Kilowatts. Since one joule = one wattxsecond, one KWxhour = 1,000watts x 3,600 seconds = 3,600,000 joules. Now calculate the electric energy cost per Joule.
So, the average is 1.5Kwatt=1500watts.How do i get the cost for one joule.
Srry, for the long post but i really need help, i tried all the problems to the extent that i know how too.
3 answers
Please post problems that are as long as yours one at a time. That way more people will see them who might have time to answer one or more.
I don't understand how you got the focal length to be 48 by multiplying 6 and 8. Those (6 and 8 mm) are the rectangular dimensions of the image. Your answer certainly does not follow from the lens maker's equation. The demagnification ratio of the 1.8 meter tall person onto the 8 mm dimension of the focal plane is 1800/8 = 225. That means di = (1/225)*do
di = 1000/225 = 4.444 mm
1/1000 + 1/4.444 = 1/f
f = 4.42 mm
That would be a very wide angle focal length setting.. not one commonly found with a zoom lens.
I don't understand how you got the focal length to be 48 by multiplying 6 and 8. Those (6 and 8 mm) are the rectangular dimensions of the image. Your answer certainly does not follow from the lens maker's equation. The demagnification ratio of the 1.8 meter tall person onto the 8 mm dimension of the focal plane is 1800/8 = 225. That means di = (1/225)*do
di = 1000/225 = 4.444 mm
1/1000 + 1/4.444 = 1/f
f = 4.42 mm
That would be a very wide angle focal length setting.. not one commonly found with a zoom lens.
There are two things wrong with this question. It asks for the cost to PRODUCE (not consume) one joule of energy. The body is NOT 100% efficient in producing energy (doing work). Most of the rest produces body heat; some becomes added weight. Also, as you noted, the cost of food per Calorie depends upon what you eat and where you eat it. Right now, I am on a 1000 Calorie a day diet that only costs about a dollar a day. Some people spend 100 times that much a day eating in restaurants.
0 answers