# Gravitational Potential Energy Project Thor

• mailmas
In summary, a proposed weapon system, Project Thor, drops a cylindrical tungsten rod from Earth orbit with a kinetic energy of 205914267929J.
mailmas

## Homework Statement

Project Thor is a proposed (and terrifying) weapon system where a cylindrical tungsten rod (19600 kg m3 ) about the size of a telephone pole (6.10 m long and 0.300 m in diameter) is dropped from Earth orbit. Imagine you dropped one of these from an orbit 10,000 km above the surface of the earth, with what kinetic energy would it hit the ground? Assume no air resistance.

## Homework Equations

m = p*Volume
KE - (mMG)/r+10000*1000 = 0
Radius Earth = 6.37 * 10^6
Mass Earth = 5.98 * 10^24

## The Attempt at a Solution

m = 19600* *6.1 * (.15)^2 * 3.1415 = 8451
PE = (mMG)/r + 10000000
= ((8451)(5.98 * 10^24)(6.67 * 10^(-11)))/((6.37 * 10^6) +10000000)
= 205914267929J

Last edited by a moderator:
I am sorry, but it is utterly unclear what you are trying to do. For example, what does this
mailmas said:
PE - (mMG)/r+10000*1000 = 0
mean? What is the 10000? What is the 1000? What makes you think this equation should hold? Also, please always write out your units. Newton is not a unit of energy.

Orodruin said:
I am sorry, but it is utterly unclear what you are trying to do. For example, what does this

mean? What is the 10000? What is the 1000? What makes you think this equation should hold? Also, please always write out your units. Newton is not a unit of energy.
Got it.
PE = -(mMG)/r
PE_initial + KE_initial = PE_final + KE_final

PE_initial = KE_final
KE = -(mMG)/r

r = Radius Earth + 10,000km
= 6.37 * 10^6m + 10,000,000m

KE = -((8451kg * (5.98 * 10^24) kg * (6.67 * 10^(-11)) m^3/s^2*kg ) / ((6.37 * 10^6) + 10,000,000)m

mailmas said:
PE_initial + KE_initial = PE_final + KE_final

PE_initial = KE_final
To get the second from the first you would need to assume that KE_initial = 0 and that PE_final = 0. This is not correct.

Orodruin said:
To get the second from the first you would need to assume that KE_initial = 0 and that PE_final = 0. This is not correct.
Okay. So the KE_initial would look like:
KE = 1/2* m* v_tangental^2
v_tangental = sqrt(G*M/r)
KE = 1/2*m*G*M/r

mailmas said:
Okay. So the KE_initial would look like:
No. If you do what the problem suggests and actually drop it from orbit, it will never fall. It will be in orbit! I believe the problem wants you to use an initial speed of zero. The problem is not in the kinetic energy. In indicating that you have zero potential energy at the end you are implicitly assuming that the Earth surface is the reference point for potential energy. Is this the case?

Orodruin said:
No. If you do what the problem suggests and actually drop it from orbit, it will never fall. It will be in orbit! I believe the problem wants you to use an initial speed of zero. The problem is not in the kinetic energy. In indicating that you have zero potential energy at the end you are implicitly assuming that the Earth surface is the reference point for potential energy. Is this the case?
Yeah it would orbit if that is the case. And I used the center of mass as the reference point so my final potential energy would be mMG/Radius Earth?

mailmas said:
And I used the center of mass as the reference point
No, you did not. Would the potential energy be zero at the center of mass if you used the expression ##V = -GMm/r##? (Note the minus sign, it is important!)

The potential energy is -GMm/r and the kinetic energy is GMm/2r so the total energy is -GMm/2r which is the energy required to leave an orbit and escape from the Earth's gravitational well to where the total energy is zero. To get an object to fall to the Earth, you would have to kill its velocity / kinetic energy in orbit. With no guidance your mass might wreck havoc but who knows where.

## 1. What is "Gravitational Potential Energy Project Thor"?

"Gravitational Potential Energy Project Thor" is a theoretical concept proposed by the US Air Force in the 1950s. It involves using the energy from a large, orbiting object to create a powerful kinetic energy weapon.

## 2. How does "Gravitational Potential Energy Project Thor" work?

The concept of "Gravitational Potential Energy Project Thor" involves launching a large object, such as a tungsten rod, into a low Earth orbit. The Earth's gravitational pull will cause the object to gain potential energy as it reaches a higher altitude. When the object is released from orbit, it will gain kinetic energy and can be directed towards a target on Earth with immense destructive force.

## 3. Is "Gravitational Potential Energy Project Thor" a feasible weapon?

While the concept of "Gravitational Potential Energy Project Thor" is theoretically possible, it is not currently a feasible weapon. The technology and resources required to launch and control such a large object in orbit are not currently available.

## 4. What are the potential risks and consequences of using "Gravitational Potential Energy Project Thor"?

The use of "Gravitational Potential Energy Project Thor" as a weapon could have catastrophic consequences. The impact of a large object traveling at high speeds could cause widespread destruction and loss of life. There are also concerns about the potential for the weapon to malfunction or be used for malicious purposes.

## 5. Are there any current projects or plans to develop "Gravitational Potential Energy Project Thor"?

As of now, there are no known active projects or plans to develop "Gravitational Potential Energy Project Thor" as a weapon. However, the concept has been revisited and discussed in recent years as a potential alternative to traditional ballistic missiles.

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