Calculate the force of gravity on a 1-kilogram box located at
a point 1.3 x 10^7 meters from the center of Earth if the force on
a 2.5-kilogram box at the same point is 6.1 newtons.
Choices
-2.44 Newtons
-3.58 Newtons
-4.87 Newtons
-8.95 Newtons

Question

Calculate the force of gravity on a 1-kilogram box located at 
a point 1.3 x 10^7 meters from the center of Earth if the force on 
a 2.5-kilogram box at the same point is 6.1 newtons.
Choices
-2.44 Newtons
-3.58 Newtons 
-4.87 Newtons 
-8.95 Newtons

shane_b · Answer

If I understand the question correctly, this should be pretty simple.  Start with:$$F=ma$$They give you an example of another object at the same point with a different mass.  Therefore, you should calculate the acceleration due to gravity at that point:$$6.1N=(2.5kg)(a)$$$$a=g=2.44m/s^2$$Knowing that you can now simply in 1kg to get the force at that point on the original object:$$F=(1.0kg)(2.44m/s^2)=2.44N$$Assuming a coordinate system where downward (towards the center) is negative, the answer would be negative.

anonymous · Answer

I see now. Thanks a million!