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Consider two copper wires of equal cross-sectional area. One wire has 3 times the length of the other. How do the resistivities of these two wires compare?

Answers

Answer 1
Answer:

Explanation:

The relation between resistance and resistivity is given by :

R=\rho (l)/(A)

\rho is resistivity of material

l is length of wire

A is area of cross section of wire

Resistivity of a material is the hidden property. If one wire has 3 times the length of the other, then it doesn't affect its resistivity. Hence, the resistivity of two wires is

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A round pipe of varying diameter carries petroleum from a wellhead to a refinery. At the wellhead, the pipe's diameter is 58.9 cm ( 0.589 m) and the flow speed of the petroleum is 12.1 m/s. At the refinery, the petroleum flows at 6.29 m/s. What is the volume flow rate of the petroleum along the pipe and what is the pipe's diameter at the refinery?

Answers

Answer:

Explanation:

The volume rate of flow = a x v where a is cross sectional area of pipe and v is velocity of flow

putting the values

π x .2945² x 12.1

= 3.3  m³ /s

To know the pipe's diameter at the refinery we shall apply the following formula

a₁ v₁ = a₂ v₂

a₁ v₁ and  a₂ v₂ are volume rate of flow of liquid which will be constant .

3.3 = a₂ x 6.29

a₂ = .5246 m³

π x r² = .5246

r = .4087 m

= 40.87 cm

diameter

= 81.74 cm

The position of a particle is given by the function x=(5t3−8t2+12)m, where t is in s. at what time does the particle reach its minimum velocity?

Answers

The particle reach its minimum velocity at time 1.06 sec.

The function is given as

x=5t^3-8t^2+12

Differentiating the above equation with respect to time, to obtain the velocity

dx/dt=v=15t^2-16t

For maximum and minimum values, put dx/dt=0

15t^2-16t=0

On solving the equation, t=0, 1.06

Therefore at time t=1.06 sec, the particle has the minimum value of velocity.

The particle reaches its minimum velocity at t = 0 s or t = 16/15 s

Further explanation

Acceleration is rate of change of velocity.

\large {\boxed {a = (v - u)/(t) } }

\large {\boxed {d = (v + u)/(2)~t } }

a = acceleration ( m/s² )

v = final velocity ( m/s )

u = initial velocity ( m/s )

t = time taken ( s )

d = distance ( m )

Let us now tackle the problem!

Given:

x = ( 5t^3 - 8t^2 + 12) ~ m

To find the velocity function, we will derive the position function above.

v = (dx)/(dt)

v = 5(3)t^(3-1) - 8(2)t^(2-1)

v = ( 15t^2 - 16t ) ~ m/s

Next to calculate the time to reach its minimum speed, then v = 0 m/s

0 = ( 15t^2 - 16t )

0 = t( 15t - 16)

\large {\boxed {t = 0 ~s ~ or ~ t = 16/15 ~ s} }

Learn more

Answer details

Grade: High School

Subject: Physics

Chapter: Kinematics

Keywords: Velocity , Driver , Car , Deceleration , Acceleration , Obstacle

If a freely falling object were somehow equipped with a speedometer, its speedreading would increase each second by
a) about 15 m/s.
b) a rate that depends on its initial speed.
c) a variable amount.
d) about 5 m/s.
e) about 10 m/s.

Answers

Answer:

  e) about 10 m/s

Explanation:

Acceleration due to gravity is nominally* 9.8 m/s². That means the change in velocity each second is ...

  (9.8 m/s²)(1 s) = 9.8 m/s ≈ 10 m/s

_____

* This is the value expected to be used in the solution of many math and physics problems. The standard value of 'g' on Earth is defined as 9.80665 m/s². It varies from place to place and with altitude. At any given place, it may also vary with time as a result of changes in mass distribution within the Earth.

A person's body is producing energy internally due to metabolic processes. If the body loses more energy than metabolic processes are generating, its temperature will drop. If the drop is severe, it can be life-threatening. Suppose that a person is unclothed and energy is being lost via radiation from a body surface area of 1.36 m2, which has a temperature of 34° C and an emissivity of 0.700. Also suppose that metabolic processes are producing energy at a rate of 122 J/s. What is the temperature of the coldest room in which this person could stand and not experience a drop in body temperature

Answers

To solve this problem it is necessary to apply the concepts related to the Stefan-Boltzman law that is responsible for calculating radioactive energy.

Mathematically this expression can be given as

P = \sigma Ae\Delta T^4

Where

A = Surface area of the Object

\sigma = Stefan-Boltzmann constant

e = Emissivity

T = Temperature (Kelvin)

Our values are given as

A = 1.36m^2

\Delta T^4 = T_2^4 -T_1^4 = 307^4-T_1^4

\sigma = 5.67*10^(-8) J/(s m^2 K^4)

P = 122J/s

e = 0.7

Replacing at our equation and solving to find the temperature 1 we have,

P = \sigma Ae\Delta T^4

P = \sigma Ae (T_2^4 -T_1^4)

122 = (5.67*10^(-8))(1.36)(0.7)(307^4-T_1^4)

T_1 = 285.272K = 12.122\°C

Therefore the the temperature of the coldest room in which this person could stand and not experience a drop in body temperature is 12°C

On a trip, you notice that a 3.50-kg bag of ice lasts an average of one day in your cooler. What is the average power in watts entering the ice if it starts at 0ºC and completely melts to 0ºC water in exactly one day 1 watt = 1 joule/second (1 W = 1 J/s) ?

Answers

Answer:

P=13.5 W

Explanation:

In this case, power is the rate of transferring heat per unit time:

P=(Q)/(\Delta t)(1)

The heat is given by the formula of the latent heat of fusion, since the ice is melting.

Q=mL_f(2)

Here m is the ice's mass and L_f is the heat of fusion of ice. Recall that one day has 86400 seconds. Replacing (2) in (1) and solving:

P=(mL_f)/(\Delta t)\nP=(3.5kg(334*10^3(J)/(kg)))/(86400s)\nP=13.5 W

Which of the following is a TRUE statement? a. It is possible for heat to flow spontaneously from a hot body to a cold one or from a cold one to a hot one, depending on whether or not the process is reversible or irreversible.
b. It is not possible to convert work entirely into heat.
c. The second law of thermodynamics is a consequence of the first law of thermodynamics.
d. It is impossible to transfer heat from a cooler to a hotter body.
e. All of these statements are false.

Answers

Answer:

e. All of these statements are false.

Explanation:

As we know that heat transfer take place from high temperature to low temperature.

It is possible to convert all work into heat but it is not possible to convert all heat in to work some heat will be reject to the surrounding.

The first law of thermodynamics is the energy conservation law.

Second law of thermodynamics  states that it is impossible to construct a device which convert all energy into work without rejecting the heat to the surrounding.

By using heat pump ,heat can transfer from cooler body to the hotter body.

Therefore all the answer is False.
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