Question

You find your mass to be $42kg$ on a weighing machine. Is your mass more or less than $42Kg$ ?

Answer 1

Hint: Recall the basics of mass of a person measured by the weighing machine. Check the forces acting on the person when he/she stands on the weighing machine. Check which of the physical quantities changes when the weight of an object changes. Hence, determine whether the mass of the person weighed by the weighing machine is more or less than the actual mass of the person.

Complete answer:
The weighing machine that we use to measure our mass actually measures our weight and then converts it into our mass and we see our mass on the scale of the weighing machine.

The weight of an object is the product of mass of the object and acceleration due to gravity. The value of the acceleration due to gravity at a place is constant. Hence, the only physical quantity changing the weight of an object is its mass.

When a person stands on the weighing machine, there are two forces acting on the person on the weighing machine. One force is the actual weight of the person acting in the downward direction and the upward thrust due to air acting in the upward direction.

Hence, the net force acting on the man standing on the weighing machine is the weight of the person. But which weight is slightly less than the actual weight of the person and this decrease in weight is equal to the upward thrust due to air.

Since the weight of the person measured by the weighing machine is less than the actual weight of the person, the mass of the person weighed by the weighing machine will be less than the actual mass of the person.

Note:
The students should not get confused by considering that the changing physical quantities in the weight of the person are the mass of the person as well as acceleration due to gravity. But we have considered the mass of the person measured by the weighing machine is at the same place. Hence, there will not be any change in acceleration due to gravity.