Question

$\huge\mathcal{Hello!}$

$\huge\textbf{Question for Physics Experts!}$

$\bold{Question-}$

What is the work done by the force of gravity on a satellite moving round the Earth ? Justify your answer .

Please tell me , what is the necessity of using ," cos 90° " in the explanation , as I'm in 9th grade , and still haven't got the concept of trigonometry .

No spamming!! ❎❎

Answer 1

Ello There!

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Question: What is the work done by the force of gravity on a satellite moving round the Earth ? Justify your answer .  

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Answer

When a sattelite moves around the earth, which is at a fixed position with only rotation, we can say that the gravtitation force that acts on the sattelite, is directed to the center of the earth. This gravtitational force acting on the satellite is perpendicular to the earth. We know that when gravtitational force acts in a perpendicular manner, the work done is 0. Therefore the work done by the gravitational force on the sattelite is 0.

(I'm 9th as well, I guess Cos90 refers to perpendicular distance)

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Hope It Helps Mate!

Answer 2

Hey dear here is your answer!!!!!

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Lemme try my best to make it simple for you to understand Aruni...

Basic things first:-

What is work done ?

→ W = F x S

Think of a situation where a satellite completes a revolution around the Earth.

What would be its Displacement ?

It would be zero because the satellite has returned to its initial position.

Therefore, S = 0

Put that in the formula and you get:-

W = F x (0)

W = 0

So, the work done is zero !

If the gravity would have done work over the satellite then it would have pulled the satellite towards the center of the Earth. But the satellites keep revolving around the Earth. That means no work is done !

The actual reason is that Gravity and Direction of Motion of the Satellite are perpendicular to each other.

That is why Work Done turns Zero.

What role does Cos 90° play:-

Cos is a concept related to triangles consisting of an angle that is 90°. It is nothing but a proportion of the Base and Hypotenuse.

Let's keep it simple...

The value of Cos 90° is Zero...

You would be clear about its proof when you study Trigonometry in Class 10th.

This concept of perpendicular and stuff is also applicable in the case of satellites since The direction of satellite is perpendicular to the gravity because the direction of the movement would be tangent to the orbit at every point which makes a straight line.

The actual formula for find the Work Done also involves the trigonometric ratios.

Therefore, we obtain:-

W = F x S x cos 90°

W = F x S x 0

W = 0

That was some complicated stuff.....

$\large\boxed{\large\boxed{\large\boxed{Easy !}}}}$

❣️⭐ Hope it helps you dear...⭐⭐❣️❣️