physics/math help please?

👨🏻‍🏫 學術台數學

[匿名]

2010-08-07 10:51 pm

yay i need help again :D haha
its just a big math review lol

im stuck on 4 physics problems.. can u please explain them to me :)

1. The base of a pyramid covers an acre of 22.8 arces (1 acre=43,560 ft ^2) and has a height of 69 feet.
find the volume of the pyramid where b is the area of the base and h is the height . (1ft =0.3048 m) answer in units of m^3

2. the following table shows the daily high temperatures for week in May

sun. 76 thurs 75
mon. 72 fri 74
tues 80 sat 78
wed75

find the net change in temperature ( the sum of all the temperature changes)

3. Assume the Sun in mostly composed of hydrogen atoms. Assume the mss of the Sun is 1.66e30 kg and the mss of a hydrogen atom is 1.672e-27. how many atoms are there in the sun?
answer in units of atoms

4 if one micrometerotite ) a sphere with a diameter on the order of 4.1e-5m) struck each square meter of the moon each second, estimate how long it would take to cover the moon to a depth of 1 m ( consider a cubic box, 1m on side , on the moon, how long would it take to fill the box?
answer in units of y. your answer must be within+ 0.1%
-

thank you so much in advance for ur help :D

更新1:

haha thanks Ed I and haha i know about the E.. i just thought it would make it easier to read :P

回答 (2)

[匿名]

2010-08-08 2:06 am

✔ 最佳答案

1.
formula for pyramid volume
V = ⅓Bh where B = area of the base, h = height of pyramid

⅓ x 22.8 acres x 69 feet
= ⅓ x (22.8 x 43560 x 0.3048²)m² x (69 x 0.3048)m
= ⅓ x (22.8 x 43560 x 69 x 0.3048³)m³
≈ 646837.8756m³

2.
net change in temperature
= final temperature - initial temperature
= temperature(sat) - temperature(sun)
= 78 - 76
= 2

3.
quantity of hydrogen atom = mass of sun / mass of hydrogen atom

1.66e30 kg / 1.672e-27 kg
= 1.66 / 1.672 x 10^(30 - -27)
≈ 0.9928 x 10^57
= 9.928 x 10^56

Note: solar mass (mass of the Sun) is (1.98892 ± 0.00025) x 10^30 kg

4.
For simplicity of calculation, assum the micrometerotite stack right on top in each layer without horizontal dislocation and the dimension does not deform under pressure.

total time
= time to fill one layer x number of layers
= (number of micrometerotite in one layer per unit area / micrometerotite rate per unit area) x (depth / height of micrometerotite layer)
= ((1 / 4.1e-5)² second x (1 / 4.1e-5)
= 1 / (4.1e-5)³ second
= 1 / (4.1e-5)³ / 60 / 60 / 24 / 365¼ year
≈ 459774 years

459774 ± 0.1%
= 459314 ~ 460234

The approximate time is 460000 years (0.049% error).

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Ed I

2010-08-08 6:00 am

1. V = (1/3)Bh = (1/3)(22.8 acres • 43560 ft^2/1 acre) (69 ft) = 22842864 ft^3 • (0.3048 m/1 ft)^3 = 646837.8756 m^3

2. -4 + 8 - 5 + 0 - 1 + 4 = +2 = net change

3. 1.66 • 10^30 kg Ã· 1.672 • 10^(-27) = 0.9928229665... • 10^57 â 9.928 •Â 10^57 atoms
By the way, e (actually E) is a calculator symbol for scientific notation and should not be used in problems or answers.

4. Sorry, I don't get this one.

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