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3 years ago

Question 25

Physics

1 answer:

aniked [119]3 years ago

7 0

Answer:

o The result of a chemical change is a different composition; in a physical change, the composition remains the same.

Explanation:

In a chemical change, new kinds of matter are produced although the atoms are the same.

For physical changes, no new kinds of matter formed. Only the state of substances changes.

Most chemical changes are usually irreversible
Physical changes are reversible in most parts.
Changes in state and form are salient characteristics of physical changes.
When new products are formed from the reactants, it is an indicator of a chemical change.

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A crowbar makes our work easier by multiplying effort true or false

OLEGan [10]

Answer:

True

Explanation:

A crowbar makes our work easier by multiply effort because it belongs to first class lever.

And first class lever makes work easier by multiplying the effort

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3 years ago

A pump is used to transport water to a higher reservoir. if the water temperature is 15ºc, determine the lowest pressure that ca

Reika [66]

Normally, the water pressure inside a pump is higher than the vapor pressure: in this case, at the interface between the liquid and the vapor, molecules from the liquid escapes into vapour form. Instead, when the pressure of the water becomes lower than the vapour pressure, molecules of vapour can go inside the water forming bubbles: this phenomenon is called cavitation.

So, cavitation occurs when the pressure of the water becomes lower than the vapour pressure. In our problem, vapour pressure at $15^{\circ}$ is 1.706 kPa. Therefore, the lowest pressure that can exist in the pump without cavitation, at this temperature, is exactly this value: 1.706 kPa.

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3 years ago

A small rock is thrown straight up with initial speed v0 from the edge of the roof of a building with height H. The rock travels

Crank

Answer:

$v_{avg}=\dfrac{3gH+v_0^2}{v_0+\sqrt{v_0^2+2gH} }$

Explanation:

The average velocity is total displacement divided by time:

$v_{avg} =\dfrac{D_{tot}}{t}$

And in the case of vertical $v_{avg}$

$v_{avg}=\dfrac{y_{tot}}{t}$

where $y_{tot}$ is the total vertical displacement of the rock.

The vertical displacement of the rock when it is thrown straight up from height $H$ with initial velocity $v_0$ is given by:

$y=H+v_0t-\dfrac{1}{2} gt^2$

The time it takes for the rock to reach maximum height is when $y'(t)=0$ , and it is

$t=\frac{v_0}{g}$

The vertical distance it would have traveled in that time is

$y=H+v_0(\dfrac{v_0}{g} )-\dfrac{1}{2} g(\dfrac{v_0}{g} )^2$

$y_{max}=\dfrac{2gH+v_0^2}{2g}$

This is the maximum height the rock reaches, and after it has reached this height the rock the starts moving downwards and eventually reaches the ground. The distance it would have traveled then would be:

$y_{down}=\dfrac{2gH+v_0^2}{2g}+H$

Therefore, the total displacement throughout the rock's journey is

$y_{tot}=y_{max}+y_{down}$

$y_{tot} =\dfrac{2gH+v_0^2}{2g}+\dfrac{2gH+v_0^2}{2g}+H$

$\boxed{y_{tot} =\dfrac{2gH+v_0^2}{g}+H}$

Now wee need to figure out the time of the journey.

We already know that the rock reaches the maximum height at

$t=\dfrac{v_0}{g},$

and it should take the rock the same amount of time to return to the roof, and it takes another $t_0$ to go from the roof of the building to the ground; therefore,

$t_{tot}=2\dfrac{v_0}{g}+t_0$

where $t_0$ is the time it takes the rock to go from the roof of the building to the ground, and it is given by

$H=v_0t_0+\dfrac{1}{2}gt_0^2$

we solve for $t_0$ using the quadratic formula and take the positive value to get:

$t_0=\dfrac{-v_0+\sqrt{v_0^2+2gH} }{g}$

Therefore the total time is

$t_{tot}= 2\dfrac{v_0}{g}+\dfrac{-v_0+\sqrt{v_0^2+2gH} }{g}$

$\boxed{t_{tot}= \dfrac{v_0+\sqrt{v_0^2+2gH} }{g}}$

Now the average velocity is

$v_{avg}=\dfrac{y_{tot}}{t}$

$v_{avg}=\dfrac{\frac{2gH+v_0^2}{g}+H }{\frac{v_0+\sqrt{v_0^2+2gH} }{g} }$

$\boxed{v_{avg}=\dfrac{3gH+v_0^2}{v_0+\sqrt{v_0^2+2gH} } }$

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3 years ago

What is the difference between revolution and rotation

Sphinxa [80]

A rotation is when the earth turns in a circle on it's axis. A revolution is the oblong path the the earth is constantly moving in around the sun. A revolution takes 365.25 days where as a rotation happens in 24 hours. <span />

8 0

3 years ago

Read 2 more answers

Please help quick! 3 questions if you answer all I will give brainliest

Nat2105 [25]

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Explanation:

4 0

3 years ago