How to evaluate work done by gravitational force when gravitational force is equal to the weight “mg” of the object which always act vertically forwards towards the earth.
Answers
Answer:
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Explanation:
With Newton’s second law, we saw that net force depends on mass and acceleration:
\vec{F}_{net}=m\vec{a}
We also know that gravity depends on the mass of the object doing the pulling (in our case, the Earth), the mass of the object being pulled (such as a person), and the distance between the two.
That’s a lot to keep track of. But if we only drop objects on (or close to) the surface of the Earth, we fix two of our three variables mentioned above (the mass of the Earth is a constant, and the distance to the object is considered a constant, since our height above the Earth’s surface is often much, much less than the radius of the Earth), and the calculation of the force of gravity becomes more manageable. And, we can even use Newton’s second law to do it!
If an object is released above the surface of the Earth, just as it begins to fall, the only force acting on it is gravity. Its free-body diagram would look like this:
This is a free-body diagram of object at the top of its trajectory, with only the force of gravity acting on it.
In our example, \vec{F}_{net} is only based on one force -- the gravitational force. So, we can write:
\vec{F}_{g}=m\vec{a}
In this special case, the acceleration of the object is caused entirely by gravity. It turns out, that when an object is close to the surface of the Earth, that value of acceleration has a very specific value, which is given a special symbol: \vec{g}. Our equation then becomes:
\vec{F}_{g}=m\vec{g}
In other words, the force of gravity on an object is the mass of the object (in kilograms) multiplied by the gravitational acceleration of the planet (in metres per second per second [down]).
But what is the value of \vec{g} on Earth?
Different objects have different values of acceleration, and you may have come up with some good reasons for this. It is commonly (but mistakenly) thought that the mass of an object changes its rate of acceleration toward the Earth -- many people think that heavier objects fall faster.