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larisa [96]
3 years ago
13

One deterrent to burglary is to leave your front porch light on all the time. If your local power utility sells energy at 17¢ pe

r kilowatt-hour, how much will it cost to leave the above lamp on for the whole week?
Physics
1 answer:
Natali [406]3 years ago
6 0
To be honest with you, there's not enough information here to calculate
the answer, because we don't know the power consumption of the front
porch light.  The best we can do is represent that as a variable ... pick a
catchy name for it, which will show up in the final answer, and then you
can 'plug in' (get it ?) whatever size light bulb you want to use over the
front porch.

OK.  First we have to give it a name.  I could use a single letter, but
that's what everybody else always does.  Remember ... this is going to
represent the power (watts) consumed by the front porch light when it's
turned on.  It's the symbol that means "Front Porch Light Power" wherever
you see it.  I could easily call it x or y or z, but I'm going to call it " FPLP ".

OK.  FPLP = power consumption of the light, in watts .

0.001 FPLP = power consumption of the light, in kilowatts (kW).

(1 week) · (7 day/week) · (24 hour/day) = 168 hours .

Energy = (power) · (time) = (0.001 FPLP) · (168 hr) = 0.168 FPLP kWhours

Cost = ($0.17 per kWh) · (number of kWh) = (2.86¢) · (FPLP) .

There it is !

For an example, if you use a 100-W bulb in the front porch light,
then FPLP=100 W.  If you leave it on 24/7 for a whole week, then
it's going to cost

        (2.86¢) · (FPLP) = (2.86¢) · (100 W)  =  $2.86
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Bond [772]
calculate\ mass\ from\ formula\ for\ density:\\\\
density=volume*mass\\
mass=\frac{density}{volume}\\\\
volume=width*length*height\\
volume=100*50*30=150000cm^3=0,15m^3\\\\
density\ of\ water=\ 999.9720 \frac{kg}{m^3} \\\\mass=0,15*999.9720=149,9958kg=149995,8grams\\\\ Answer\ is\ :\\water\ which\ weight\ is\ equal\ to\ 149995,8grams.

4 0
3 years ago
Neutron stars are extremely dense objects that are formed from the remnants of supernova explosions. Many rotate very rapidly. S
Alja [10]

Answer:

16294 rad/s

Explanation:

Given that

M(ns) = 2M(s), where

M(s) = 1.99*10^30 kg, so that

M(ns) = 3.98*10^30 kg

Again, R(ns) = 10 km

Using the law of gravitation, the force between the Neutron star and the sun is..

F = G.M(ns).M(s) / R²(ns), where

G = 6.67*10^-11, gravitational constant

Again, centripetal force of the neutron star is given as

F = M(ns).v² / R(ns)

Recall that v = wR(ns), so that

F = M(s).w².R(ns)

For a circular motion, it's been established that the centripetal force is equal to the gravitational force, hence

F = F

G.M(ns).M(s) / R²(ns) = M(s).w².R(ns)

Making W subject of formula, we have

w = √[{G.M(ns).M(s) / R²(ns)} / {M(s).R(ns)}]

w = √[{G.M(ns)} / {R³(ns)}]

w = √[(6.67*10^-11 * 3.98*10^30) / 10000³]

w = √[2.655*10^20 / 1*10^12]

w = √(2.655*10^8)

w = 16294 rad/s

7 0
3 years ago
The sound intensity of a certain type of food processor in normally distributed with standard deviation of 2.9 decibels. If the
Maru [420]

Answer: (48.41,\ 52.19)

Explanation:

The confidence interval for population mean is given by :-

\overline{x}\pm z_{\alpha/2}\dfrac{\sigma}{\sqrt{n}}

Given : Sample size : n=9

Sample mean : \ovreline{x}=50.3\text{ decibels}

Standard deviation : \sigma=2.9\text{ decibels }

Significance level : \alpha=1-0.95=0.05

Critical value : z_{\alpha/2}=z_{0.025}=1.96

Now, the 95% confidence interval estimate of the (true, unknown) mean sound intensity of all food processors of this type :-

50.3\pm (1.96)\dfrac{2.9}{\sqrt{9}}\\\\\approx50.3\pm1.89\\\\=(50.3-1.89,\ 50.3+1.89)=(48.41,\ 52.19)

6 0
3 years ago
What speed would a proton need to achieve in order to circle Earth 1790 km above the magnetic equator, where the Earth's mag- ne
irinina [24]

Answer:

The velocity is 31.25 m/s and direction is toward west.

Explanation:

Given that,

Distance h= 1790 km = 1.790\times10^{6}\ m

Magnetic field B=4\times10^{-8}\ T

Mass of proton m=1.673\times10^{-21}\ Kg

Radius of earth R =6.38\times10^{6}\ m

Radius of orbit r=R+h

r=6.38\times10^{6}+1.790\times10^{6}

r=8170000\ m

We need to calculate the speed

Using formula of magnetic field

Bvq=\dfrac{mv^2}{r}

v=\dfrac{Bqr}{m}

Put the value into the formula

v=\dfrac{4\times10^{-8}\times1.6\times10^{-19}\times8170000}{1.673\times10^{-21}}

v=31.25\ m/s

Hence, The velocity is 31.25 m/s and direction is toward west.

6 0
3 years ago
Which of the following surfaces reflects the most light
Gre4nikov [31]

Answer:

D

Explanation:

it could be the yellow cloth but we see are shadow on the sidewalk most of the time and shadows are made from reflecting light so your answer should be D

3 0
3 years ago
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