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3 years ago

13

A 3kg book falls from a shelf. If it lands with a speed of 4.8 m/s, from what height did it fall? A. 28.8 m , B. 1.2 m , C. 0.6

m , D. 14.1 m

1 answer:

Irina-Kira [14]3 years ago

7 0

The correct answer is B. 1.2 m (apex)

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A horizontal force of 20 N is applied to the object. Will the force applied make the object move?

goldenfox [79]

It depends on two factors: The direction of application of force and the coefficient of friction, $\mu$ , between the object and the surface on which the object is placed.

If the direction of application of force is vertically downwards, then the object will not move for any value of $\mu$ .

If the coefficient of friction is zero, $\mu=0$ , then any value of force that is not in a vertically downward direction, the object will move.

If the direction of application of force is not vertically downwards, then it depends on the value of frictional force.

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3 years ago

An instructor’s laser pointer produces a beam of light with a circular cross section of diameter 0.900 mm and a total power outp

il63 [147K]

Answer:

$E_0 = 2180.53N/C.$

$B_0 = 7.27*10^{-6}T.$

$U_{avg} = 4.2*10^{-5}J/m^3.$

Explanation:

The Intensity $I$ of the beam is

$I = P /A$

The diameter of the beam is 0.900mm; therefore, the area is

$A = \pi( \dfrac{0.900*10^{-3}}{2} )^2$

$A = 6.36*10^{-7}m^2$

and since $P = 4.00*10^{-3}W$ , the intensity of the beam is

$I = \dfrac{4.00*10^{-3}W}{6.36*10^{-7}m^2}$

$\boxed{I = 6289.3W/m^2.}$

Now, the intensity $I$ is related to $E_0$ by the relation

$I = \dfrac{E_0^2}{2\mu_0 c}$

solving for $E_0$ we get

$E_0 = \sqrt{2\mu_0 c I}$

putting in the numbers we get:

$E_0 = \sqrt{2(1.26*10^{-6}) (3*10^8) (6289.3)}$

$\boxed{E_0 = 2180.53N/C.}$

The amplitude of magnetic field $B_0$ is related to $E_0$ by

$B_0 = \dfrac{E_0}{c}$

putting in numerical values we get:

$B_0 = \dfrac{2180.53}{3*10^8}$

$\boxed{B_0 = 7.27*10^{-6}T. }$

The average energy density of the laser light is

$U_{avg} = \epsilon_0 E_0^2$

$U_{avg} = (8.85*10^{-12}) (2180.53)^2$

$\boxed{U_{avg} = 4.2*10^{-5}J/m^3.}$

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4 years ago

Tracy's foot is pushing on her cars gas pedal, is it pushing or pulling back?

UkoKoshka [18]

Answer:

pushing

Explanation:

7 0

2 years ago

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An old lady sits on and pushes down on a park bench. What is the reaction force? A. The bench pushes up on her. B. The Earth pul

Vladimir [108]

B the earth pulls down because of gravity

3 0

4 years ago

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If you push a crate across a factory floor at constant speed in a constant direction, what is the magnitude of the force of fric

poizon [28]

Answer:

The magnitude of the force of friction equals the magnitude of my push

Explanation:

Since the crate moves at a constant speed, there is no net acceleration and thus, my push is balanced by the frictional force on the crate. So, the magnitude of the force of friction equals the magnitude of my push.

Let F = push and f = frictional force and f' = net force

F - f = f' since the crate moves at constant speed, acceleration is zero and thus f' = ma = m (0) = 0

So, F - f = 0

Thus, F = f

So, the magnitude of the force of friction equals the magnitude of my push.

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3 years ago