Describe the heliocentric model of the universe

1 answer:

6 0

The heliocentric model of the universe was proposed by Nicolaus Copernicus. There are numerous scientist in ancient times who try to explain what happens in the universe. He may not be the first one who proposed that what astronomical body is the center of the universe. However, he stated that the center of the universe was the sun, not the earth. And the earth revolves around it. It is in his book on the Revolutions of the Heavenly Bodies. It was only published as he lay in his deathbed.

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A tradesman sharpens a knife by pushing it with a constant force against the rim of a grindstone. The 30-cm-diameter stone is sp

Lorico [155]

Answer:

a. 0.21 rad/s2

b. 2.205 N

Explanation:

We convert from rpm to rad/s knowing that each revolution has 2π radians and each minute is 60 seconds

200 rpm = 200 * 2π / 60 = 21 rad/s

180 rpm = 180 * 2π / 60 = 18.85 rad/s

r = d/2 = 30cm / 2 = 15 cm = 0.15 m

a)So if the angular speed decreases steadily (at a constant rate) from 21 rad/s to 18.85 rad/s within 10s then the angular acceleration is

$\alpha = \frac{\Delta \omega}{\Delta t} = \frac{21 - 18.85}{10} = 0.21 rad/s^2$

b) Assume the grind stone is a solid disk, its moment of inertia is

$I = mR^2/2$

Where m = 28 kg is the disk mass and R = 0.15 m is the radius of the disk.

$I = 28*0.15^2/2 = 0.315 kgm^2$

So the friction torque is

$T_f = I\alpha = 0.315*0.21 = 0.06615 Nm$

The friction force is

$F_f = T_f/R = 0.06615 / 0.15 = 0.441 N$

Since the friction coefficient is 0.2, we can calculate the normal force that is used to press the knife against the stone

$N = F_f/\mu = 0.441/0.2 = 2.205 N$

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3 years ago

What are the three subatomic particles of an atom?

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Protons, neutrons, and electrons are the three main subatomic particles found in an atom. Protons have apositive (+) charge. An easy way to remember this is to remember that both proton and positive start with theletter "P." Neutrons have no electrical charge.

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1. How many atoms are needed to form a molecule? Answer:

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Answer: 20

Explanation: cause

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