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zaharov [31]
3 years ago
7

2. If a rock fell down a cliff and hit the bottom of the ravine at 4 seconds, how fast was the rock

Physics
2 answers:
Iteru [2.4K]3 years ago
6 0

Answer: -39.2 m/s or 39.2 m/s directed downwards

Explanation:

This situation is a good example of Free Fall, where the main condition is that the initial velocity must be zero V_{o}=0, and the acceleration is constant (acceleration due gravity).

So, in order to calculate the final velocity V of the rock just at the moment it hitsthe bottom of the cliff, we will use the following equation:

V={V_{o}}^{2}+gt

Where:

g=-9.8 m/s^{2} is the acceleration due gravity (directed downwards)

t=4 s is the time it takes to the rock to fall down the cliff

V=(-9.8 m/s^{2})(4 s)

V=-39.2 m/s This is the rock's final velocity and its negative sign indicates it is directed downwards

Marina CMI [18]3 years ago
6 0

Explanation:

It is given that,

Initial speed of the rock, u = 0

It hits the bottom of the ravine at 4 seconds. Let v is the speed of the rock when it hits the bottom of the cliff. It will move under the action of gravity. Using equation of kinematics as :

v=u+at

a = g

v=u+gt

v=gt

v=9.8\ m/s^2\times 4\ s

v = 39.2 m/s

So, the speed of the rock when it hit the bottom of the cliff is 39.2 m/s. Hence, this is the required solution.

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Elemental analysis of the unknown gas from part a revealed that it is 30.45% n and 69.55% o by mass. What is the molecular formu
Anna71 [15]

Answer:

the molecular formula for the gas is NO₂

Explanation:

since it contains

Nitrogen = n → 30.45%

Oxygen = o → 69.55%

and 30.45%+69.55% = 100% , then the gas only contains nitrogen and oxygen

Also we know that the proportion of oxygen over nitrogen  is

proportion of oxygen over nitrogen  = moles of oxygen / moles of nitrogen

since

moles = mass / molecular weight

then for a sample of 100 gr of the unknown gas

mass of oxygen = 69.55%*100 gr = 69.55 gr

mass of Nitrogen = 30.45%*100 gr = 30.45 gr

proportion of oxygen over nitrogen = (mass of oxygen/ molecular weight)/(mass of nitrogen / molecular weight of nitrogen ) =  (69.55 gr/ 16 gr/mol) /( 30.45 gr /14 gr/mol) = 1.998 mol of O/ mol of N≈ 2 mol of O/ mol of N

therefore there are 2 atoms of oxygen per atom of nitrogen

thus the molecular formula for the gas is:

NO₂

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3 years ago
Two sacks contain the same number of identical apples and are separated by a distance r. The two sacks exert a gravitational for
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Answer:

Explanation:

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Name three characteristics of scientists that are important to their work but are also found in nonscientists.
Alina [70]

Answer:

The three characteristics of a good scientist are his curiosity, creativity and problem-solving skills.

Explanation:

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2 years ago
How much momentum will a dumb-bell of mass 10 kg transfer
frosja888 [35]

We want to find how much momentum the dumbbell has at the moment it strikes the floor. Let's use this kinematics equation:

Vf² = Vi² + 2ad

Vf is the final velocity of the dumbbell, Vi is its initial velocity, a is its acceleration, and d is the height of its fall.

Given values:

Vi = 0m/s (dumbbell starts falling from rest)

a = 10m/s² (we'll treat downward motion as positive, this doesn't affect the result as long as we keep this in mind)

d = 80×10⁻²m

Plug in the values and solve for Vf:

Vf² = 2(10)(80×10⁻²)

Vf = ±4m/s

Reject the negative root.

Vf = 4m/s

The momentum of the dumbbell is given by:

p = mv

p is its momentum, m is its mass, and v is its velocity.

Given values:

m = 10kg

v = 4m/s (from previous calculation)

Plug in the values and solve for p:

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6 0
3 years ago
How have the competing explanations' experiments on atoms affected the development of the atomic model?
zaharov [31]

Answer:Competing explanations' experiments on atoms gave a perfect modal of an atom

Explanation

There is a long story of atom. Different scientist gave different theories related to atomic modal but no one individually gave a perfect modal they perfect each other work and finally we got a perfect modal of atom.

Here is a short story of atom

in 400 B.C.E, Democritus was the first philosopher who gave the concept of atom. He believes that everything is made up of tiny spheres  and these spheres are known as atoms.

in 1803, Dalton said that atoms of an element are similar. For example all atoms of carbon are similar.

in 1904 J. J. Thomson proposed that atom is sphere in which positively charged matter is filled and electrons are randomly scattered in that positively charged matter.

in 1911, Rutherford gave the concept of nucleus he believed that at the center of atoms all positively charged  particles are present and this center is known as nucleus. He said that negatively charge electrons revolves around the nucleus in particular orbit.

In 1913, Niels Bohr gave a new model he believes that atomic model is similar to planetary modal. He believed that the electrons in an atom revolves around  the nucleus in sets of orbits in a similar manner like the planets revolves around the sun.

In 1919, Rutherford gave the concept of proton.  

In 1932, James Chadwick gives the concept of neutron.

In this way different scientist gave different theories related to atoms and finally they all gave a perfect modal of atom.

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