Question

# What is the weight, in Newton, of an object on mercury with a mass of 90 kilograms?

Hint:The weight of an object is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity $w = mg$ for an object in free fall, So that gravity is the only force acting on it, then the expression for weight follows from Newton's second law.
We know that $Weight = Mass - Acceleration\,due\,to\,gravity$
At mercury acceleration due to gravity is $= 36m/\sec 2$
$= 90kg \times 3.6m/{\sec ^2}$
$= 324\,$Newton
Weight of $90kg$object on earth will weight $324$ Newton on Mercury
Note: An object that has a mass of 1kg weight about$9.8$Newton So if you already known the mass of an object and you want to know its weight in Newton, you simply Multiply the No. of kilogram by $9.8$ Newton. Conversely if you know the object weight in Newton, you can divide by $9.8$ Newton and yours get that object’s mass. .