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nadya68 [22]
3 years ago
10

A pencil is dropped from the roof of the school what is the speed after 3s down is the negative direction.

Physics
2 answers:
allsm [11]3 years ago
8 0
On Earth, the acceleration due to gravity is (-9.8 meters per second) per second.

If the school, the roof, and the pencil are on Earth,
then after 3 seconds, the pencil's speed is

[ (-9.8 meters per second)/second ] times [ 3seconds ] = <u>-29.4 meters per second </u>
uysha [10]3 years ago
4 0
You have to use 1st equation of motion v = u +at as distance(s) is not given.....
as pencil is dropped from rest therefore u = 0m/s and accleration due to gravity is = -9.8 m/s
v = 0 - (9.8)(3)
v = -29.4 m/s
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Explanation:

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3 years ago
What is the maximum power that can be delivered by a 1.4-cm-diameter laser beam propagating through air
Aleksandr-060686 [28]

Complete Question

The maximum electric field strength in air is 4.0 MV/m. Stronger electric fields ionize the air and create a spark. What is the maximum power that can be delivered by a 1.4-cm-diameter laser beam propagating through air

Answer:

The  value  is  P = 3.270960 *10^{6} \  W

Explanation:

From the question we are told that

   The  electric field strength is  E  = 4.0 \  M \  V/m  =  4.0 *10^6 \  V/m

    The  diameter is  d =  1.4 \  cm  = 0.014 \ m

Generally the radius is mathematically represented as

        r = \frac{d}{2}

=>     r = \frac{0.014}{2}

=>    r   = 0.007 \  m

Generally the cross-sectional area is mathematically represented as

        A =  \pi r^2

        A =  3.142 *  (0.007)^2

       A = 0.000154 \ m^2

Generally the maximum power that can be delivered is mathematically represented as

        P = \frac{c *  \epsilon_o  *  E^2 *  A }{2}

Here c is the speed of light with value  c =  3.0*10^{8} \  m/s

        \epsilon_o is the permittivity of free space with value  \epsilon_o  =  8.85 *10^{-12}  \ m^{-3} \cdot kg^{-1}\cdot  s^4 \cdot A^2

     P =  \frac{3,0*10^8 *  8.85*10^{-12} *  (4 *10^6)^2 * 0.00154}{ 2}

       P = 3.270960 *10^{6} \  W

         

5 0
3 years ago
Copper wire of diameter 0.289 cm is used to connect a set of appliances at 120 V, which draw 1850 W of power total. The resistiv
vodka [1.7K]

Answer:

(a) The power wasted for 0.289 cm wire diameter is 15.93 W

(b) The power wasted for 0.417 cm wire diameter is 7.61 W

Explanation:

Given;

diameter of the wire, d = 0.289 cm = 0.00289 m

voltage of the wire, V = 120 V

Power drawn, P = 1850 W

The resistivity of the wire, ρ = 1.68 x 10⁻⁸ Ω⋅m

Area of the wire;

A = πd²/4

A = (π x 0.00289²) / 4

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(a) At 26 m of this wire, the resistance of the is

R = ρL / A

R = (1.68 x 10⁻⁸  x 26) / 6.561 x 10⁻⁶

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P = IV

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I = 15.417 A

Power wasted = I²R

Power wasted = (15.417²)(0.067)

Power wasted = 15.93 W

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d = 0.417 cm = 0.00417 m

A = πd²/4

A = (π x 0.00417²) / 4

A = 1.366 x 10⁻⁵ m²

Resistance of the wire at 26 m length of wire and  1.366 x 10⁻⁵ m² area;

R = ρL / A

R = (1.68 x 10⁻⁸  x 26) / 1.366 x 10⁻⁵

R = 0.032 Ω

Power wasted = I²R

Power wasted = (15.417²)(0.032)

Power wasted = 7.61 W

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Which of the following shows kinetic energy being converted into potential energy?
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