Help with physics grav force

In summary, the conversation is about someone seeking help with physics related questions. They are specifically asking for assistance with determining the speed of an object before impact using the formulas of Conservation of Energy. A suggestion is given to use the formulas -GMm/x and -GMm/R + 1/2mv^2 and equate them to solve. Another person jumps in to provide additional information about the formulas for gravitational potential energy and the gravitational field strength of the Earth. However, they also mention that mgh is only applicable for heights smaller than the radius of the Earth and advise the original poster to start their own thread instead of adding a new question to an existing one.
  • #1
laker_gurl3
94
0
help with physics! grav force

hello can someone help me on these questions?
i just need help with which formulas to use, i could not get any answer at all.

a stationary 25 kg object is released from a position 8.9x10^6m from the center of the earth. what's is the speed of the object before impact?
 
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  • #2
Apply Conservation Of Energy.Before and after the impact.

Initially Total Energy: [itex]- \frac {GMm}{x}[/itex]

Final Energy : [itex]- \frac {GMm}{R}[/itex] + [itex]\frac{1}{2}mv^2[/itex]

Equate above and Solve.

BJ
 
  • #3
I am a year 12 student so please bear with me - I could be horribly wrong.

PS: this is my first post on this forum!

You need to figure out the change in gravitational potential energy from the height you gave, to the surface of the earth.

You need to know that
the formula for for grav. potential energy is given by mgh
radius of Earth is 6.3*10^6m ( I think? )
gravitational field strength of Earth is given by GM/(R^2)


Lets figure out the G part of mgh at the greater height
[(6.67*10^-11)*25000] / ((8.9*10^6)^2)
that is.. G M / R ^2

equals 2.11*10^-20

subsitute that into MGH...

= mgh...
= 25000 * (2.11*10^-20) * (8.9*10^6)
gpe at greater height = 4.7 * 10^-9 Joules


the gravitational field strength at the Earth's surface is 9.8N/kg
so the GPE at surface of the Earth is

= M G H
= 25000 * (9.8*25) * (6.3*10^6)

equals ? something that doesn't look right?

this is converted to Kinetic Energy??... i think? oh god.. I am ready to get flamed badly
 
Last edited:
  • #4
bumclouds said:
I am a year 12 student so please bear with me - I could be horribly wrong.

PS: this is my first post on this forum!

You need to figure out the change in gravitational potential energy from the height you gave, to the surface of the earth.

You need to know that
the formula for for grav. potential energy is given by mgh
radius of Earth is 6.3*10^6m ( I think? )
gravitational field strength of Earth is given by GM/(R^2)


Lets figure out the G part of mgh at the greater height
[(6.67*10^-11)*25000] / ((8.9*10^6)^2)
that is.. G M / R ^2

equals 2.11*10^-20

subsitute that into MGH...

= mgh...
= 25000 * (2.11*10^-20) * (8.9*10^6)
gpe at greater height = 4.7 * 10^-9 Joules


the gravitational field strength at the Earth's surface is 9.8N/kg
so the GPE at surface of the Earth is

= M G H
= 25000 * (9.8*25) * (6.3*10^6)

equals ? something that doesn't look right?

this is converted to Kinetic Energy??... i think? oh god.. I am ready to get flamed badly


mgh is only applicable for heights appreciably smaller than radius of the earth.

BJ
 
  • #5
And please don't add a new question to someone else's thread- start your own thread.
 

What is the formula for calculating gravitational force?

The formula for calculating gravitational force is F = Gm1m2/r^2, where F is the force, G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between the two objects.

What is the difference between mass and weight in terms of gravitational force?

Mass is the amount of matter in an object, while weight is the measure of the force of gravity on an object. Mass is constant, while weight can vary depending on the strength of the gravitational force acting on the object.

How does distance affect gravitational force?

The force of gravity decreases as the distance between two objects increases. This relationship is known as the inverse square law, which means that the force is inversely proportional to the square of the distance between the objects.

What is the role of the gravitational constant in calculating gravitational force?

The gravitational constant, denoted by G, is a universal constant that represents the strength of the gravitational force. It is used in the formula for calculating gravitational force and is necessary for determining the force between two objects of known mass and distance.

How does the mass of the objects affect gravitational force?

The greater the mass of two objects, the greater the force of gravity between them. This means that the more massive an object is, the stronger its gravitational pull will be on other objects.

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