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OLga [1]
3 years ago
13

A joule is an amount of energy, and a watt is a rate of using energy, defined as 1 W = 1 J / s. How many joules of energy are re

quired to run a 100 W light bulb for one day?
Coal has about 30E6 J of energy per kg, but a power plant can only use 30% of this energy to make electricity (i.e., it is 30% efficient). How many kilograms of coal have to be burned to light a 100 W light bulb for one day?
Physics
1 answer:
Naily [24]3 years ago
4 0
How many joules of energy are required to run a 100 W light bulb for one day?

<span><span><span>A</span><span>100 </span>joules</span><span><span>B</span>100<span>W </span><span>× </span>24<span>hr </span>joules</span><span><span>C</span>100<span>W </span><span>× </span>24<span>hr </span><span>× </span>60<span>min∕hr </span>joules</span><span><span>D</span>100<span>W </span><span>× </span>24<span>hr </span><span>× </span>60<span>min∕hr </span><span>× </span>60<span>s∕min </span>joules</span></span>
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The Earth’s surface, on average, carries a net negative charge (while the clouds and lower atmosphere carry a net positive charg
LenaWriter [7]

Answer:

(a) Q = -6.765 * 10⁵ C ; σ = 1.33 * 10⁻⁹ C/m²

(b) 0.23 N/C

Explanation:

(a) Electric field at the surface of a sphere is given as:

E = kQ/r²

Where

k = Coulombs constsnt

Q = charge

r = radius of sphere

To find charge Q, we make Q subject of the formula:

Q = (E * r²)/k

Hence, charge, Q, at the surface of the earth, having radius, r = 6.371 * 10⁵ and electric field, E = 150 N/C is:

Q = [150 * (6.371 * 10⁶)²] / (9 * 10⁹)

Q = 6.765 * 10⁵ C

Since we're told that the charge at the earth's surface is negative,

Q = -6.765 * 10⁵ C

Surface charge density, σ, given as:

σ = |Q|/A

Where

|Q| = magnitude of charge

A = surface area.

Surface area, A, of the earth is given as:

A = 4πr²

A = 4π * (6.371 * 10⁶)²

A = 510064471909788 m²

σ = 6.765 * 10⁵/510064471909788

σ = 1.33 * 10⁻⁹ C/m²

(b) At a height 5km from the earth's surface, the electric field will be:

E = kQ/(r + 5km)²

r + 5km = 6376km = 6.376 * 10⁶m

=> E = (9 * 10⁹ * 6.765 * 10⁵)/(6.376 * 10⁶)²

E = 149.77 N/C

The difference between the electric field at the surface of the earth and at a height of 5km is:

159 - 149.77 N/C = 0.23 N/C

3 0
3 years ago
A boat with a horizontal tow rope pulls a water skier. She skis off to the side, so the rope makes an angle of 12.0 ∘ with the f
Sladkaya [172]

Answer:

62.601kJ

Explanation:

We have a force with a horizontal component given by the angle of 15°. So wue can take this component to calculate the total work done, that is,

W_T = Fd(cos\theta)

Our values are,

d=320m

Angle = 12\°

Force=200N,

Substituting in Work equation,

W_T = 200(320)(cos12)

W_T = 62601.4J

W_T = 62.601kJ

4 0
2 years ago
What type of wave is produced when you move one end of a horizontal spring up and down?
Volgvan
A. a transverse wave is produced
7 0
3 years ago
A chair of weight 125 N lies atop a horizontal floor; the floor is not frictionless. You push on the chair with a force of F = 3
iris [78.8K]

Answer:

N = 148.10N

Explanation:

GIVEN

Weight =125 N

force = 35

angle =42°

since there is no vertical acceleration a_{y} = 0 from

free body diagram

\Sigma fa_{y} = ma_{y} = 0

N-W-Fsin42\degree = 0\\\\N= W+Fsin42\\N = 125+35\times 0.66\\N = 148.10 N

5 0
3 years ago
Laser transmissions travel at a higher speed than the radio waves true or false
uranmaximum [27]
<span>False. Laser transmissions and radio waves are both forms of electromagnetic radiation. Both travel at approximately 3.00 x 10^8 meters per second. This is the case because wavelength and frequency are directly proportional to this value. Although laser light has a shorter wavelength than radio waves, it will travel at the same speed because the frequency will be greater.</span>
6 0
3 years ago
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