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Vlad1618 [11]
3 years ago
11

A 4kg block sitting on the floor, how much potential energy does it have?

Physics
2 answers:
aniked [119]3 years ago
8 0
P.E.=mgh

P.E.= mass×gravity×height, therefore 4kg×10×0= 0 J

K.E. is also equal to 0 because the block is not moving, is in the state of Inertia
prohojiy [21]3 years ago
3 0

Well, there you have a very important principle wrapped up in that question.

There's actually no such thing as a real, actual amount of potential energy.
There's only potential <em><u>relative to some place</u></em>.  It's the work you have to do
to lift the object from that reference place to wherever it is now.  It's also
the kinetic energy the object would have if it fell down to the reference place
from where it is now.

Here's the formula for potential energy:    PE = (mass) x (gravity) x (<em><u>height</u></em><u>)</u> .

So naturally, when you use that formula, you need to decide "height above what ?"

If you're reading a book while you're flying in a passenger jet, the book's PE is
(M x G x 0 meters) relative to your lap, (M x G x 1 meter) relative to the floor of the
plane, (M x G x 10,000 meters) relative to the ground, and maybe (M x G x 25,000 meters)
relative to the bottom of the ocean.

Let's say that gravity is 9.8 m/s² .

Then a 4kg block sitting on the floor has (39.2 x 0 meters) PE relative to the floor
it's sitting on, also (39.2 x 3 meters) relative to the floor that's one floor downstairs,
also (39.2 x 30 meters) relative to 10 floors downstairs, and if it's on the top floor of
the Amoco/Aon Center in Chicago, maybe (39.2 x 345 meters) relative to the floor
in the coffee shop that's off the lobby on the ground floor. 

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Answer:

λ = 2.7608 x 10⁻⁷ m = 276.08 nm

Explanation:

The work function of a metallic surface is the minimum amount of photon energy required to release the photo-electrons from the surface of metal. The work function is given by the following formula:

Work Function = hc/λ

where,

Work Function = (4.5 eV)(1.6 x 10⁻¹⁹ J/1 eV) = 7.2 x 10⁻¹⁹ J

h = Plank's Constant = 6.626 x 10⁻³⁴ J.s

c = speed of light = 3 x 10⁸ m/s

λ = longest wavelength capable of releasing electron.

Therefore,

7.2 x 10⁻¹⁹ J = (6.626 x 10⁻³⁴ J.s)(3 x 10⁸ m/s)/λ

λ = (6.626 x 10⁻³⁴ J.s)(3 x 10⁸ m/s)/(7.2 x 10⁻¹⁹ J)

<u>λ = 2.7608 x 10⁻⁷ m = 276.08 nm</u>

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3 years ago
Engineers are designing a curved section of a highway. If the radius of curvature of the curve is 194 m, at what angle should th
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Answer:

The banking angle is 23.84 degrees.

Explanation:

Given that,

Radius of the curve, r = 194 m

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On the banked curve, the centripetal force is balanced by the force of friction such that,

mg\ tan\theta=\dfrac{mv^2}{r}

tan\theta=\dfrac{v^2}{rg}

tan\theta=\dfrac{(29)^2}{194\times 9.8}

\theta=23.84^{\circ}

So, the banking angle is 23.84 degrees. Hence, this is the required solution.    

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A cylinder with rotational inertia I₁ = 2.4 kg · m² rotates clockwise about a vertical axis through its center with angular spee
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Explanation:

Given that.

First cylinder data

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angular speed ω₁ = 5.8 rad/s.

Second cylinder data

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angular speed ω₂ = 7.0 rad/s.

If the cylinders couple so they have the same rotational axis, what is the angular speed of the combination (in rad/s)?

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ω = 23.02 / 3.7

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The combine angular speed of the cylinder is 6.22 rad/s

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