How many newtons does a 3.8 kg backpack weigh on Earth and on the moon?

Weight is a measure of the pull exerted on an object by
gravitational pull. The weight is measured in kilograms in S.I.Units. One kilogram
weight is defined as the force exerted on one kilogram mass by the gravitational force
acting on surface of earth. In kilogram mass is equal to the matter contained in 1 liter
of water at 4 degrees centigrade.

The weight of an object,
when measured in terms of newtons, is same as the force exerted on it due to gravity.
This is equal to mass in kilogram multiplied by acceleration due to
gravity.

Using the above insights we calculate the required
quantities as follows.

1) Weight on
earth:

Weight on earth in newtons = Mass x (Acceleration
due to gravity on earth)

= 3.8 x 9.8 = 37.24
N

2) Weight on moon:

Weight on
earth in newtons = Mass x (Acceleration due to gravity on
moon)

= 3.8 x (9.8/6) = 6.2067
N

Note: Gravitational force on moon is approximately 1/6
times that on earth.