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Nana76 [90]
3 years ago
10

A) How many joules of energy does a 100-watt light bulb use per hour? Express your answer using two significant figures.

Physics
1 answer:
kenny6666 [7]3 years ago
5 0

A) 3.6\cdot 10^5 J

The power used by an object is defined as

P=\frac{E}{t}

where

E is the energy used

t is the time elapsed

In this problem, we have

P = 100 W is the power of the light bulb

t = 1 h = 3600 s is the time elapsed

Solving for E, we find the amount of energy used by the light bulb:

E=Pt = (100 W)(3600 s)=3.6\cdot 10^5 J

B) 1.1 \cdot 10^2 m/s

The kinetic energy of an object is given by

K=\frac{1}{2}mv^2

where

m is the mass

v is the speed of the object

In this problem, we have a man of mass

m = 65 kg

we want its kinetic energy to be

E=3.6\cdot 10^5 J

Therefore, we can calculate its speed from the previous formula:

v=\sqrt{\frac{2K}{m}}=\sqrt{\frac{2(3.6\cdot 10^5 J)}{65 kg}}=105.2 m/s = 1.1 \cdot 10^2 m/s

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The amount of light that enters the pupil is controlled by the:<br> retina.<br> lens.<br> inis.
nignag [31]

Answer: The amount of light that enters the pupil is controlled by the Iris

Explanation:

5 0
3 years ago
A spacecraft is moving past the earth at a constant speed of 0.60 times the speed of light. The astronaut measures the time inte
Afina-wow [57]

Answer:

the time interval that an earth observer measures is 4 seconds

Explanation:

Given the data in the question;

speed of the spacecraft as it moves past the is 0.6 times the speed of light

we know that speed of light c = 3 × 10⁸ m/s

so speed of spacecraft v = 0.6 × c = 0.6c

time interval between ticks of the spacecraft clock Δt₀ = 3.2 seconds

Now, from time dilation;

t = Δt₀ / √( 1 - ( v² / c² ) )

t = Δt₀ / √( 1 - ( v/c )² )

we substitute

t = 3.2 / √( 1 - ( 0.6c / c )² )

t = 3.2 / √( 1 - ( 0.6 )² )

t = 3.2 / √( 1 - 0.36 )

t = 3.2 / √0.64

t = 3.2 / 0.8

t = 4 seconds

Therefore, the time interval that an earth observer measures is 4 seconds

6 0
3 years ago
a. When the electric field between the plates is 75% of the dielectric strength and energy density of the stored energy is 2800
Olegator [25]

Answer: The value of the dielectric constant k = 1.8

Explanation:

If C= ε A/d and

Electrostatic energy W = 1/2CV^2

Substitutes C in the first formula into the energy formula.

W = 1/2 ε A/d × V^2

Let us remember that electric field strength E is the ratio of potential V to the distance d. Where V = Ed

Substitute V = Ed into the energy W.

W = 1/2 × ε A/d ×( Ed )^2

W = 1/2 × ε A/d × E^2 × d^2

d will cancel one of the ds

W = 1/2 × ε Ad × E^2

W/Ad = 1/2 × ε × E^2

W/V = 1/2 × ε E^2

Where Ad = volume V

E = dielectric strength

εo = permittivity of free space = 8.84 x 10^-12 F/m

W/V = 2800 J/m^3

Let first calculate the dielectric strength

2800 = 1/2 × 8.84×10^-12 × E^2

5600 = 8.84×10^-12E^2

E^2 = 5600/8.84×10^-12

E = sqrt( 6.3 × 10^14)

E = 25 × 10^7

75% of E = 18.9 × 10^6Jm

The permittivity of the material will be achieved by using the same formula

2800 = 1/2 × ε E^2

2800 = 0.5 × ε × (18.9×10^6)^2

2800 = ε × 1.78 × 10^14

ε = 2800/1.78×10^14

ε = 1.57 × 10^-11

Dielectric constant k = relative permittivity

Relative permittivity is the ratio of the permittivity of the material to the permittivity of the vacuum in a free space. That is

k = 1.57×10^-11/8.84×10^-12

k = 1.776

k = 1.8 approximately

Therefore, the value of the dielectric constant k is 1.8

3 0
3 years ago
How far will a car travel if its velocity is 15 m/s in 3 seconds? Follow example below.
svet-max [94.6K]
<h3><u>Solution</u><u>:</u></h3>
  • Distance (d) = 112 m
  • Time (t) = 4 seconds
  • Let the speed be v.
  • We know, speed = Distance / Time
  • Therefore, v = d/t

or, v = 112 m ÷ 4 s = 28 m/s

<h3><u>Answer</u><u>:</u></h3>

<u>The </u><u>speed </u><u>of </u><u>the</u><u> </u><u>cheetah</u><u> </u><u>is </u><u>2</u><u>8</u><u> </u><u>m/</u><u>s.</u>

4 0
2 years ago
A fossil form when an organism buried in sediment dissolves leaving a hollow area
IceJOKER [234]

Answer:

A Mold

Explanation:

A mold forms when hard parts of an organism are buried in sediment; the hard parts completely dissolve over time, leaving behind a hollow area. A cast forms as a result of a mold when minerals and sediment fill in the impression.

3 0
3 years ago
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