Question

What is net force on a bathroom scale when a $100\,kg$ person stands on it? ( $g = 10m{\sec ^{ - 2}}$ )

Answer 1

Hint: In order to solve this question we need to understand force and its type. Force is defined as push or pull in a body which causes a state change in body motion and it is mathematically defined by Newton's second law, which states that force is equal to rate of change of momentum of body.

Complete step by step answer:
Force is of four types, first is gravitational force, by which two masses attract each other, second is electromagnetic force, which acts between two charges and it can be attractive and repulsive depending on sign of charge, third is strong nuclear force and fourth is weak natural force, both these forces act inside nucleus of atom.

Mass of the body is given as, $M = 100\,kg$. Acceleration of a body is in downward direction since body is attracted by force of gravity, so acceleration is equal to, $a = g$
$a = 10\,m\,{\sec ^{ - 2}}$
So From newton's second law, force is given as, $F = ma$
Putting values we get,
$F = (100\,kg)(10\,m\,{\sec ^{ - 2}})$
$\Rightarrow F = 1000\,kg\,m\,{\sec ^{ - 2}}$
$\therefore F = 1000\,N$

So, net force on the bathroom scale is, $F = 1000\,N$.

Note:It should be remembered that bathroom scales actually measures the reaction by earth when you are pushing the earth with some force, it is evident from the newton’s third law of motion that for every action there is equal and opposite reaction, so earth presses you back when you push the earth. If you do not push the earth for example if you could measure your weight on bathroom scales in air then it would not show no reading, as here you are not pushing anything.