What went wrong in calculating the mass of planet Mongo?

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In summary, the conversation discusses a scenario where the chief scientist-engineer measures the acceleration of a stone thrown upward from the ground on the planet Mongo. After calculating the gravity force and using the general formula for force due to gravity, the scientist-engineer realizes they have made a mistake in their calculations. They then discuss possible solutions and conclude that the initial velocity of the stone should be halved to achieve a more accurate result. Ultimately, the conversation centers around finding the mass of the planet Mongo.
  • #1
ninjagowoowoo
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Q:
Your starship, the Aimless Wanderer, lands on the mysterious planet Mongo. As chief scientist-engineer, you make the following measurements: a 2.50-kg stone thrown upward from the ground at 15.0 m/s returns to the ground in 7.00 s; the circumference of Mongo at the equator is 1×10^5 km; and there is no appreciable atmosphere on Mongo. What is the mass of Mongo?

well i started out by finding the acceleration of the rock. I used V=V_o + at and from the problem, v_o = 15, and t=7.

Then I used F=ma to get the gravity force.

Then I used the general formula for force due to gravity. from the problem I used: R=1*10^5 / 2*pi (because they gave us the circumference) everything else is pretty self-explanitory. Since I have F, G, the mass of the rock, and R, I solved for M and got the wrong answer. Could anyone tell me where I went wrong?
 
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  • #2
I used V=V_o + at and from the problem, v_o = 15, and t=7.
How do you know v?
 
  • #3
It would help a little if you put some numbers in. A shot in the dark:
If you got an acceleration of gravity (a) that is less than [itex]4\frac{m}{s^2}[/itex] then you calculated that incorrectly.
 
  • #4
thrown upward from the ground at 15.0 m/s returns to the ground in 7.00 s
Is this not an acceptable value for v_o? and, if it returned to the ground, wouldn't v be 0?
 
  • #5
Is this not an acceptable value for v_o? and, if it returned to the ground, wouldn't v be 0?

No, v would take that value for maximum height.
 
  • #6
...yeah I got a value less than 4...
 
  • #7
So to get the equation to work out, I would just halve the time right? That would give me a V=0 at the max height. and an A of about 4.3m/s
 
  • #8
Thanks a lot for the help guys, I got it now.
 
  • #9
Berislav said:
How do you know v?
V = -V_o (?)
 
  • #10
V = -V_o (?)
The OP didn't state that, which lead me to think that he overlooked it.
 

1. What is a rock thrown on planet Mongo?

A rock thrown on planet Mongo refers to any object that is thrown or propelled through the air on the fictional planet Mongo, which is often depicted in science fiction stories and movies.

2. What is the significance of throwing rocks on planet Mongo?

In many science fiction stories, throwing rocks on planet Mongo symbolizes the primitive or violent nature of the inhabitants of the planet. It is also often used as a form of defense or attack in battles.

3. Can rocks be thrown on any other planet besides Mongo?

Yes, rocks can be thrown on any planet with a solid surface and atmosphere, as long as there is enough force to overcome the gravitational pull of the planet.

4. How is throwing rocks on planet Mongo different from throwing rocks on Earth?

The main difference is the gravity and atmospheric conditions on planet Mongo compared to Earth. The gravity on planet Mongo may be stronger or weaker, and the atmosphere may be thicker or thinner, affecting the trajectory and distance of the thrown rock.

5. What are some potential dangers of throwing rocks on planet Mongo?

As with throwing rocks on any planet, there is a risk of injury or damage to objects or structures. Additionally, on planet Mongo, there may be other dangers such as hostile creatures or advanced technology that can intercept and redirect thrown rocks.

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