# Help needed on a weight and mass problem!

1. Dec 6, 2005

### avb203796

A large animal with a mass of 1500kg is weighed on the surface of the Earth. What is its weight in N? If the animal steps off of the scale and down to the Earth 150 cm below, what force does the animal exert on the Earth at this point, and what is the resulting acceleration of the Earth upwards toward the animal?

I understand hear that w=mg therefore I get that if wof the animal on Earth would = (1500kg)(9.80m/s^2)=14700N but beyond that I have no idea how to determine the forces. Please help!

2. Dec 6, 2005

### vaishakh

The anmal exerts it weight on the earth. as a reaction, following the Newton's third law, earth exerts a force bak on animal. This force is called the normal force. Since the normal force keeps the animal in vertical equilibrium it must equal its weight and must be acted upon in an upward direction. A much more important point, in mechanics two objects are said to be in contact onl if a normal force acts between them. So now you have got enough information to answer the last question

3. Dec 8, 2005

### avb203796

So then does this mean that the force the animal exerts on the Earth would be a -14700N and the force the Earth exerted back would be a positive 14700N? Alos, what acceleration would the animal cause to a planet with the gravitational acceleration and mass of the moon? I am not familiar wiht the mass and gravitational accelaration of the moon, does anyone know what these values are because I can solve that last question if I have the values. Which would move the most toward the animal, the earth or the moon? Justify your answer with equations/calculation. Can you determine the ratio of the distances moved by the Earth and the moon-like planet toward the animal? I don not really understand what is being asked of me in the last couple of questiosn so I do not know how to solve them.

4. Dec 8, 2005

### vaishakh

I cannot see any question about moon in your first post and hence i cannot understand about what you are talking.
Ihave given you enough of information to answer your question. If no, then go through your first post and find the differences between the question you need help and the one you typed.
Anyway no need of a question mark about the result, that is true.

If you need the gravitational acceleration of the objects in moon is 6 times less than earth-almost 1.6

5. Dec 9, 2005

### gunblaze

Perphaps u could give the title of the topic u are going through..
Is it Dynamics, forces or gravitation? Or perphaps try rephrase the qn?

6. Dec 13, 2005

### avb203796

This is the full question however, I understand how to solve the begining it is just the stuff about the moon that is confusing me. A large animal with a mass of 1500kg is weighed on the surface of the Earth. What is its weight in N? If the animal steps off of the scale and down to the Earth 150 cm below, what force does the animal exert on the Earth at this point, and what is the resulting acceleration of the Earth upwards toward the animal?
Alos, what acceleration would the animal cause to a planet with the gravitational acceleration and mass of the moon? Which would move the most toward the animal, the earth or the moon? Justify your answer with equations/calculation. Can you determine the ratio of the distances moved by the Earth and the moon-like planet toward the animal? I don not really understand what is being asked of me in the last couple of questiosn so I do not know how to solve them.