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Tpy6a [65]
3 years ago
13

A person is standing outdoors in the shade where the temperature is 17 °C. (a) What is the radiant energy absorbed per second by

his head when it is covered with hair? The surface area of the hair (assumed to be flat) is 140 cm2 and its emissivity is 0.87. (b) What would be the radiant energy absorbed per second by the same person if he were bald and the emissivity of his head were 0.68?
Physics
1 answer:
Inessa05 [86]3 years ago
7 0

Answer:

a) 4.9W b) 3.82W

Explanation:

Stefan-Boltzmann law of radiation formulae:

Q/t (W) = sigma* e*A*T^4

Sigma = 5.67*10^-8 j/sm^2K^4 (Stefano Boltzmann constant)

e = emissivity

T = absolute temperature in kelvin and A = area in m^2

a) Q/t = 140/10000(m^2) * 0.87* 5.67* 10^-8* (290^4) = 4.9W

b) without hair the

Q/t = 140/ 10000(m^2) *0.68* 5.67* 10^-8* (290^4)

= 3.82W

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3 years ago
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Josh starts his sled at the top of a 2.9-m-high hill that has a constant slope of 25∘. After reaching the bottom, he slides acro
algol13

Answer:

S=48.29 m

Explanation:

Given that the height of the hill h = 2.9 m

Coefficient of kinetic friction between his sled and the snow μ = 0.08

Let u be the speed of the skier at the bottom of the hill.

By applying conservation of energy at the top and bottom of the inclined plane we get.

Potential Energy=kinetic Energy

mgh = (1/2) mu²

u² = 2gh

u²=2(9.81)(2.9)

   =56.89

u=7.54 m/s

a = - f / m

a = - μ*m*g / m

a = - μg

From equation of motion

v²- u² = 2 -μ g S

v=0 m/s

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S=48.29 m

3 0
3 years ago
Calculate the momentum of a 1800 kg elephant charging a hunter at a speed of 7.50 m/s.
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The amount of movement, linear momentum, momentum or momentum is a physical quantity derived from a vector type that describes the movement of a body in any mechanical theory. In classical mechanics, the amount of movement is defined as the product of body mass and its velocity at a given time.

p= mv

Where,

m = mass

v = Velocity

Our values are given as,

m = 1800kg

v = 7.5m/s

Replacing we have that,

p = (1800)(7.5)

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8 0
3 years ago
1. While John is traveling along an interstate highway, he notices a 160-mile marker as he passes through town. Later John passe
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Number of miles that marker shows when passes through town= 160 miles.

Number of miles that marker shows currently to John = 115 miles.

We need to find the distance between town and John's current location.

For the problem, we can clearly see that Town is at 160 miles away but when John passes the marker shows 115 miles.

So, it's just the difference between 160 miles and 115 miles.

In order to find that difference, we need to subtract those two numbers.

160miles - 115miles = 45 miles.

So, we could say the distance between town and John's current location is 45 miles.

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3 years ago
As a diligent physics student, you carry out physics experiments at every opportunity. At this opportunity, you carry a 1.33 m l
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Answer: 62 μT

Explanation:

Given

Length of rod, l = 1.33 m

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