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3 years ago

An object that is in free fall seems to be ______

Physics

1 answer:

bekas [8.4K]3 years ago

3 0

An object that is in free fall seems to be (D) weightless.

Objects which are in free fall are said to be weightless because they only have the force of gravity acting upon them. Objects in free fall do not experience air resistance.

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Two concrete spans of a 380 m long bridge are

Mazyrski [523]

Answer:

4.163 m

Explanation:

Since the length of the bridge is

L = 380 m

And the bridge consists of 2 spans, the initial length of each span is

$L_i = \frac{L}{2}=\frac{380}{2}=190 m$

Due to the increase in temperature, the length of each span increases according to:

$L_f = L_i(1+ \alpha \Delta T)$

where

$L_i = 190 m$ is the initial length of one span

$\alpha =1.2\cdot 10^{-5} ^{\circ}C^{-1}$ is the temperature coefficient of thermal expansion

$\Delta T=20^{\circ}C$ is the increase in temperature

Substituting,

$L_f=(190)(1+(1.2\cdot 10^{-5})(20))=190.0456 m$

By using Pythagorean's theorem, we can find by how much the height of each span rises due to this thermal expansion (in fact, the new length corresponds to the hypothenuse of a right triangle, in which the base is the original length of the spand, and the rise in heigth is the other side); so we find:

$h=\sqrt{L_f^2-L_i^2}=\sqrt{(190.0456)^2-(190)^2}=4.163 m$

4 0

4 years ago

how much water is needed to produce 1kwh of electricity at a power plant that is 30% efficient if the temperature increase 10 C

Dimas [21]

The amount of water needed is 287 kg

Explanation:

The amount of energy that we need to produce with the power plant is

$E=1 kWh = (1000W)(1h)=(1000W)(3600s)=3.6\cdot 10^6 J$

We also know that the power plant is only 30% efficient, so the energy produced in input must be:

$E_{in}=\frac{E}{0.30}=\frac{3.6\cdot 10^6}{0.3}=1.2\cdot 10^7 J$

The amount of water that is needed to produce this energy can be found using the equation

$E_{in}=mC\Delta T$

where:

m is the amount of water

$C=4186 J/kg^{\circ}C$ is the specific heat capacity of water

$\Delta T=10^{\circ}C$ is the increase in temperature

And solving for m, we find:

$m=\frac{E_{in}}{C\Delta T}=\frac{1.2\cdot 10^7}{(4186)(10)}=287 kg$

Learn more about specific heat capacity:

brainly.com/question/3032746

brainly.com/question/4759369

#LearnwithBrainly

3 0

3 years ago

Water waves of wavelength 4m are produced by two generators S1 and S2.

Vaselesa [24]

A is not the correct answer because the amplitude and oscillation and there is 1/2 A in oscillation

8 0

2 years ago

Anyone know how to solve this? 4+9×2÷3−1

Nutka1998 [239]

You want to use PEMDAS to solve this equation.

4+9*2/3-1

4+18/6-1

4+6-1

10-1

Your answer is 9

Thanks -John

If you have anymore question just ask! :)

5 0

3 years ago

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column.

zheka24 [161]

Answer:

1. Molecular cloud

2. Close binary

3. Brown dwarf

4. Protostellar wind

5. Thermal pressure

6. Protostellar disk

7. Jet

8. Degeneracy pressure

Explanation:

1. The Sun formed, probably along with other stars, within a large molecular cloud.

2. A Close binary consists of two stars that orbit each other every few days.

3. A Brown dwarf is a "star" so small in mass that its core never gets hot enough to sustain nuclear fusion reactions.

4. Most of the gas remaining from the process of star formation is swept into interstellar space by a protostellar wind.

5. As a protostar's internal temperature increases, its growing thermal pressure helps slow its contraction due to gravity.

6. Planets may form within the protostellar disk that surrounds a forming star.

7. Mass can be lost through a jet of material ejected along a protostar's axis of rotation.

8. A "star" with mass below 0.08 solar mass has its gravitational contraction halted by degeneracy pressure.

8 0

3 years ago