Mercury Gravity question

[kevodfx]

Hello,

 

I am attmepting to assist my son with his science homework. We have repeatedly struck out on the question I am posting below. I would wait until we could figure it out, but because his homework is automated and will not let him continue until he get's this question correct, we are falling seriously behind. Please point me in the correct direction.

Mercury has a mass of 3.30 X 10²³ kg. Its radius is 2,440 km. What would the weight (in newtons) of a 25 kg object be on the surface of Mercury?

 

Thank you for your help.

 

Kevin

[swansont]

You want to use Newton's law of gravity, F = GMm/r^2

 

The force is the weight, and G is Newton's gravitation constant.

[Rajnish Kaushik]

it would me only 35.5 kg approx

[imatfaal]

it would me only 35.5 kg approx

 

The answer should be in Newtons (the SI unit of force) not Kilograms (an SI unit of mass).

 

And remember to get everything in the right unit before doing your calculation. To get newtons out - you want to put in metres, kilograms, and G in the normal format.

 

F = (G M m) / r^2

 

N = ([N (m/kg)^2] . [kg].[kg]) / [m^2]

[swansont]

Also the purpose of HW help is to point people in the right direction not just give them the answer.