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3 years ago

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Which statements accurately describe Dmitri Mendeleev’s contributions to the development of the periodic table? Check all that a

pply.
Mendeleev wrote the first modern chemistry textbook.
Mendeleev produced the first orderly arrangement of known elements.
Mendeleev ordered the elements by increasing atomic number.
Mendeleev used patterns to predict undiscovered elements.
Mendeleev accounted for variations resulting from isotopes.

2 answers:

ipn [44]3 years ago

8 0

Answer:

2 & 4

Explanation:

?

Mama L [17]3 years ago

6 0

Mendeleev produced the first orderly arrangement of known elements. Mendeleev used patterns to predict undiscovered elements.

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A woman can row a boat at 4.0 mph is still water.

vovikov84 [41]

Answer:

1) $\theta=120^{\circ}$ from the positive x-axis.

2) $t=20\ min$

Explanation:

Given:

speed of rowing in still water, $v=4\ mph$

1)

speed of water stream, $v_s=2\ mph$

we know that the direction of resultant of the two vectors is given by:

$tan\ \beta=\frac{v.sin\ \theta}{v_s+v.cos\ \theta}$

where:

$\beta=$ the angle of resultant vector from the positive x-axis.

$\theta =$ angle between the given vectors

When the rower wants to reach at the opposite end then:

$\beta =90^{\circ}$

so,

$tan\ 90^{\circ}=\frac{v.sin\ \theta}{v_s+v.cos\ \theta}$

$\Rightarrow v_s+v.cos\ \theta=0$

$2+4\times cos\ \theta=0$

$cos\ \theta=-\frac{1}{2}$

$\theta=120^{\circ}$ from the positive x-axis.

2)

Now the resultant velocity of rowing in the stream:

$v_r=\sqrt{v^2+v_s^2+2\times v.v_s.cos\ \theta}$

$v_r=\sqrt{4^2+2^2+2\times 4\times 2\times cos\ 120}$

$v_r=12\ mph$

Therefore time taken to cross a 4 miles wide river:

$t=\frac{4}{12}$

$t=\frac{1}{3}\ hr$

$t=20\ min$

8 0

3 years ago

A 0.12 g honeybee acquires a charge of +24pC while flying. The earth's electric field near the surface is typically 100 N/C, dow

shusha [124]

Answer:

150000000

$\dfrac{F_e}{F_g}=0.00000203873598369$

49050000 N/C

Explanation:

q = Charge = 24 pC

m = Mass of honeybee = 0.12 g

E = Electric field = 100 N/C

g = Acceleration due to gravity = 9.81 m/s²

$1\ C=6.25\times 10^{18}\ electrons$

Number electrons is

$n=24\times 10^{-12}\times 6.25\times 10^{18}\\\Rightarrow n=150000000$

The number of electrons added or removed was 150000000

Force is given by

$F_e=Eq\\\Rightarrow F_e=100\times 24\times 10^{-12}\\\Rightarrow F_e=2.4\times 10^{-9}\ N$

The ratio is

$\dfrac{F_e}{F_g}=\dfrac{2.4\times 10^{-9}}{0.12\times 10^{-3}\times 9.81}\\\Rightarrow \dfrac{F_e}{F_g}=0.00000203873598369$

The ratio is $\dfrac{F_e}{F_g}=0.00000203873598369$

Balancing the forces we get

$Eq=mg\\\Rightarrow E=\dfrac{mg}{q}\\\Rightarrow E=\dfrac{0.12\times 10^{-3}\times 9.81}{24\times 10^{-12}}\\\Rightarrow E=49050000\ N/C$

The electric field required is 49050000 N/C

4 0

4 years ago

A positive test charge of 8.5 × 10 negative 7 Columbus experiences a force of 4.1 × 10 negative 1 N calculate the electric field

Sophie [7]

Explanation:

direction of electric field is same as that of force experienced by the test charge

8 0

3 years ago

A 20 kg box has 1000 joules of potential energy on a shelf. How high is the shelf?

navik [9.2K]

Formula: PE = mgh
m = 20 kg, g = 9.8 m/s^2 h= ?
1000 = 20 * 9.8 * h
1000 = 196h
h = 5.10204082
The height is around 5m

5 0

3 years ago

When a charge is discharged to the earth, we call it?

Tems11 [23]

Answer:

lightning

Explanation:

correct answer is Lightning because it is the naturally occurring electrostatic discharge, during 2 electrically charge field in atmosphere and on the ground temporarily equalize themselves and they instantly release energy.
As it is released cloud so we called it lightning but a spark is generated when the electric field strength is sufficient to ionize the molecules of air, creating a small conduction path through the air.
This is usually a cascade process, because free electrons accelerate in the electric field and ionize more molecules by colliding.

3 0

3 years ago