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3 years ago

Which situation describes the highest rate of power?

Physics

1 answer:

Darya [45]3 years ago

8 0

Answer : The correct option is, (D) A machine does 400 joules of work in 5 seconds.

Explanation :

Power : It is defined a the rate of doing work per unit time.

Formula used :

$P=\frac{w}{t}$

where,

P = power

w = work done

t = time

Now we have to determine the rate of power for the following options.

(A) A machine does 200 joules of work in 10 seconds.

$P=\frac{200}{10}=20W$

(B) A machine does 400 joules of work in 10 seconds.

$P=\frac{400}{10}=40W$

(C) A machine does 200 joules of work in 5 seconds.

$P=\frac{200}{5}=40W$

(D) A machine does 400 joules of work in 5 seconds.

$P=\frac{400}{5}=80W$

From this we conclude that, a machine does 400 joules of work in 5 seconds has the highest rate of power.

Hence, the correct option is, (D)

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Birds resting on high-voltage power lines are a common sight. the copper wire on which a bird stands is 1.28 cm in diameter and

nekit [7.7K]

Answer:

$8\cdot 10^{-4} V$

Explanation:

First of all, let's find the cross-sectional area of the copper wire. The radius of the wire half the diameter:

$r=\frac{d}{2}=\frac{1.28 cm}{2}=0.64 cm=6.4\cdot 10^{-3} m$

So the area is

$A=\pi r^2 = \pi (6.4\cdot 10^{-3} m)^2=1.29\cdot 10^{-4} m^2$

Now we can calculate the resistance of the piece of copper wire between the bird's feet, with the formula:

$R=\rho \frac{L}{A}$

where

$\rho=1.68\cdot 10^{-8} \Omega m$ is the resistivity of copper

$L=4.12 cm=4.12 \cdot 10^{-2} m$ is the length of the piece of wire

$A=1.29\cdot 10^{-4} m^2$ is the cross-sectional area

Substituting, we find

$R=(1.68\cdot 10^{-8} m^2)\frac{4.12\cdot 10^{-2} m}{1.29\cdot 10^{-4} m^2}=5.4\cdot 10^{-6} \Omega$

And since we know the current in the wire, I=149 A, we can now find the potential difference across the body of the bird, by using Ohm's law:

$V=IR=(149 A)(5.4\cdot 10^{-6} \Omega)=8\cdot 10^{-4} V$

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3 years ago

The volume of a rectangular prism is given by the formula V = lwh, where l is the length of the prism, w is the width, and h is

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the volume of the box is:
All the expressions given.

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