What is the magnitude of normal force acting on 75kg child?

Question

What is the magnitude of normal force acting on 75kg child?

Please show work, if possible. Thanks.

Answer 1

If the MASS of the child is 75kg and the child is on a horizontal surface, the normal force is 75*gN. If the WEIGHT of the child is 75kg, the normal force is 75N. If the weight is what is meant, the units given should have been kgwt. 1kgwt = 1N. This is confusing because we tend to use weight and mass as meaning the same thing. If we place an object on a scale, and the mass of the object is 1kg, the scale should read 1N, not 1kg; unfortunately the scales are not made that way, and we have to be careful about what we mean when we say that an object weighs a certain amount.

Answer 2

depends on if the child is accelerating (e.g. in an accelerating car, or elevator). If not, then its just the force of gravity. But "normal" force would imply than the child might be standing on an incline. If the child is not accelerating, and is standing on a level surface, then just use F=mg.