20 Physics -- Gravitation

Which takes more fuel, a voyage from the earth to the moon or from the moon to the earth?

1 Answers

The gravitational potential energy of a voyager of mass m at a distance r from the earth is where M is the mass of the earth. The gravitational potential energy of the voyager at a distance r from the moon is where M_moon is the mass of the moon. As r and m are constants and M > M_moon, then numerically, W > W_moon, i.e. the work needed to make a voyage from the earth to the moon is greater than that from the moon to the earth. So it takes more fuel to make the voyage from the earth to the moon

A fighter plane flying horizontally at an altitude of 1.5 km with speed 720 km/h passes directly overhead an anti-aircraft gun. At what angle from the vertical should the gun be fired for the shell...

When an air bubble rises in water, what happens to its potential energy?

Why does the moon revolve around the earth but not the sun? (even if the gravitational force between the sun and moon is twice of the gravitational force between the earth and the moon.)

We know that the gravitational force of attraction keeps the moon revolving around the earth, and the earth revolving around the Sun. However, recall that for the moon to escape the bound of the earth’s gravitational force and fall under the influence of the Sun’s gravity, it must possess a certain velocity. This is what is known as escape velocity.

Determine a relation for the escape velocity by equating the centripetal force of attraction between the moon and the earth and the gravitational...

Calculate the distance below and above the surface of the earth, at which the value of acceleration due to gravity becomes ¼ th of that at earth’s surface?

Formula Setup:

g at height h from the Earth's surface = g' = g (R/(R+h))^2
g at depth h below the Earth's surface = g' = g(1 - h/R)

To find: h where g' = g/4

At height h above the Earth's surface:

g' = g(R/(R+h))^2

g/4 = g (R/(R+h))^2

1/4 = (R/(R+h))^2

1/2 = R/(R+h)

R + h = 2R

h = 2R - R

So, h = R

At depth h above the Earth's surface:

g' = g (1 - h/R)

or, g/4 = g (1 - h/R)

or, 1/4 = 1 - h/R

or, h /R = 1- 1/4

or, h/R = 3/4

So, h = 3R/4

Hence, at height h = R above the Earth's surface and at a depth h = 3R/4...

Define centre of mass and centre of gravity? When will they be equal?

A hypothetical point at which the whole mass of a body is considered to be concentrated is known as centre of mass.

While the hypothetical point at which whole weight of a body is considered to be concentrated is known as centre of gravity.

As we know weight is g times the mass of the body and g decreases with altitude, if we ignore this variation of g over the vertical dimension of body(I e. in uniform gravitational field), then it's centre of mass and centre of gravity will be equal.

What is gravity

Gravity is just another name for Gravitation. However, it differs from Gravitation in a sense that it is an attractive force between a very large and a very small body. For example: the attraction between the Earth and a body is called gravity because the mass of Earth is very much greater than that of the body.

What is interstellar space? What is the energy of a body in interstellar space?

What happens to the velocity of a body when it escapes the Earth's surface? Assume that the body has been sent with an initial velocity equal to escape velocity. Is this journey acceleration or ret...

What is the difference between Centre of gravity and Centre of mass of a system?

The centre of gravity of a body is defined as the point where the whole weight of the body can be supposed to act.

The centre of mass of a body is the point the where the whole mass of the of the body can be supposed to be concentrated.

For regular bodies, the C.G and C.M. coincide but, for a body of large dimension. The value of g is different for its different parts, the C.M may not coincide with C.G. At a gravity free space, C.G. makes no sense but C.M. has still meaning.

Under what circumstances would your weight become zero ?

The weight of an object or entity, in the physical sense, would generally become zero under the circumstances of being in a weightless environment, such as in outer space or during freefall.