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2 years ago

what will be the focal lenght of a combined lens made by contact of two lenses of power +3D and -2D.

Physics

1 answer:

4vir4ik [10]2 years ago

3 0

P_1=+3D
P_2=-2D

$\\ \bull\tt\dashrightarrow P=P_1+P_2$

$\\ \bull\tt\dashrightarrow P=+3D-2D=+1D$

Now

$\\ \bull\tt\dashrightarrow f=\dfrac{1}{P}$

$\\ \bull\tt\dashrightarrow f=\dfrac{1}{1}$

$\\ \bull\tt\dashrightarrow f=1m$

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Complete question:

A child sits in a wagon with a pile of 0.64-kg rocks. If she can throw each rock with a speed of 7.5 m/s relative to the ground, causing the wagon to move, how many rocks must she throw per minute to maintain a constant average speed against a 3.9-N force of friction

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The number of rocks per minutes thrown is 49 rocks/min

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Given;

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$F_a$ is the applied force

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Substitute the given parameters;

$\frac{N}{t} = \frac{f_k}{mv}\\\\ \frac{N}{t} = \frac{3.9}{0.64*7.5}\\\\ \frac{N}{t} = 0.8125 \ \frac{rocks}{second} * \frac{60 \ seconds}{1 \ min} = 48.75 \ \frac{rocks}{min} \$

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3 years ago

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2 years ago

what will be the focal lenght of a combined lens made by contact of two lenses of power +3D and -2D.​

what will be the focal lenght of a combined lens made by contact of two lenses of power +3D and -2D.