Help on a simple question (1 Viewer)

[Sirius Black]

A person stood on scales thqat were designed for the Earth whilst on Mars. The scale gave a reading of 50kg. Would the actual mass of the person be 50kg since the mass is independent of the location of the body right?
the part which confused me is that the basic principle involves in the scales actually measure our weight. Could anyone explain the answer to the q above plz?
Thanx in advance.

 

[KFunk]

The person's mass would be greater I think. If you consider that the scales are designed for earth then the scales respond to the force and give you a reading of your mass. To give you this reading on earth it has to, effectively, divide your weight force by 9.8.

Consider your weight force on earth to be W_e and your weight force on mars to be W_m. Then W_m < W_e since gravity is less on mars (I believe).

Your mass reading is obtained by dividing your weight force by 9.8 so your mass reading on earth = W_e/9.8 and your mass reading on mars = W_m/9.8 .

But, W_m < W_e so
W_m/9.8 < W_e/9.8

i.e your mass reading on mars < your proper mass reading on earth

Unless I've misunderstood how a scale works that should be a general way to reason it out, albeit long.

 

[Antwan23q]

...which confused me is that the basic principle involves in the scales actually measure our weight. Could anyone explain the answer to the q above plz?
Thanx in advance.

The scales measure the actual weight, but its calibrated to read the mass of it.

 

[helper]

The persons mass will be the same but the scales will change what they read due to the calibration.

They read 50kg on Mars, means there is F=mg=50*9.8=490N pushing down on them (based on Earth's calibration).
To find your mass Fnet=490=mg(mars) As g mars is 3.77.
490=m*3.77
m=130kg

 

[Sirius Black]

They read 50kg on Mars, means there is F=mg=50*9.8=490N pushing down on them (based on Earth's calibration).
To find your mass Fnet=490=mg(mars) As g mars is 3.77.
490=m*3.77
m=130kg

wait a minute, I am getting more confused now. How could the man have same weight (net force) on both planets with diff. g?

 

[helper]

He doesn't.
The scales are calibrated for Earth. When they read 50kg, they have a net Force equal that of the weight force caused by a 50 kg mass on Earth. That is the first calculation. To determine what the net force is. The 50kg is not the real mass. It also isn't his weight on Earth.

As the net Force is equal to the Weight on Mars, where it is being measured. You can then calculate the mass of the object.

This is the mass the scales would read if they were on Earth.
The weight on Earth would be W=mg=130*9.8-=1272N