Simple question that needs an answer (1 Viewer)

[underthesun]

Questions

1. You buy a sanyo weight scale, designed for earth.

2. You bring it to moon.

3. The scale reads 40 kg as you stand on it.

Assuming that that the gravity on the moon is 6 times less, what is your mass?

(i'd say 240 kg, but my teacher is saying it remains 40kg)....

 

[EvilIsAnArtForm]

mass always stays they same doesn't it...and weight changes bcos weight is a force...so ur weight is 40kg or ur mass is that????....cos if ur weight is 40 kg then ur mass would be something else F=ma 40=(9.8/6) x m, m = 40/(9.8/6) = around 24...but i think i wasted my time typing all that cos i'm prob wrong anyway

 

[Constip8edSkunk]

Whats a sanyo weight scale?

as evil said the mass is always the same

however scales such as the bathroom/kitchen scales, spring measure ments all measure the weights, and this is affected by the gravity of the environments and in these cases, it will mean that your mass is = the weight/force (N) measured / gravitational acceleration = 400/(9.8/6) ~ 245kg

those balancing scales on the otherhand measures the mass through its calibrations and gravity does not affect this in any way, therefor it will measure your mass as 40kg.

 

[Huy]

Question 1 of the CSSA was similar

50kg for that one, so 40kg for this one.

 

[underthesun]

Originally posted by Constip8edSkunk
Whats a sanyo weight scale?

well i was just affected by consumerism .

my argument

The scale reads 40 kg. It does not mean the mass is 40 kg.

If you voted 40kg, then something is wrong. Bringing the scale to the moon, you should weigh less no? Especially it's designed for earth..

Originally posted by Huy
Question 1 of the CSSA was similar

50kg for that one, so 40kg for this one.

it's CSSA, i just altered it so that no-one that hasn't done CSSA knows

two person from my class hasn't done it. But it;s unlikely they'll come here anwyays..

 

[jims]

anyway, for that cssa question, it cant be 50kg because it says that the scale was designed for earth, so that would mean that it is calibrated to convert weight into mass according to the gravity of earth. so on uranus, or watever planet it was, its reading would be lighter than the real weight, wouldnt it?
same thing for this question.

ed: this aint going to help em in that test

 

[underthesun]

Originally posted by jims
anyway, for that cssa question, it cant be 50kg because it says that the scale was designed for earth, so that would mean that it is calibrated to convert weight into mass according to the gravity of earth. so on uranus, or watever planet it was, its reading would be lighter than the real weight, wouldnt it?
same thing for this question.

ed: this aint going to help em in that test

i'd go a bravo, however teacher (mine) insists that it's 50 kg. That's the strange part... did CSSA do a mistake?

 

[jims]

yeh well our school changed it because its so damn stoopid.

actually, i think our school changed about 3 of the answers.

 

[Huy]

Yeah, we had a discussion about this question.

Your mass remains constant, and if the question asks for mass, then it'll be 50 (or 40 in this case). But your weight-force (W=mg), as measured on the 'Earth-scale' has been designed for Earth. Now, if you took it to Mars (or wherever), then you'll have less weight, but the same mass.

We had a few 'stupid' CSSA questions this year.
1. This scale/mass question
2. Solarcells and intensity/emf vs threshold frequency (but the answer is intensity/emf because it refers to Einstein's postulate about photons and EM waves being quantised, but both are 'correct', however increasing intensity increases the emf produced is 'more correct' as it was relating to Einstein)

Then there was Q16.
About mass-length contraction.
Everything was 'wrong' with that question, so we're going to get the marks for that, depending on our answer.

(I'm sure people would have finished CSSA already, since it was a while ago, and other schools are doing Independent papers).
I'll edit my post if required.

 

[underthesun]

Originally posted by Huy
Your mass remains constant,

but they didn't specify a mass, they just said "it weighted 50 using a scale designed for earth". Do you happen to know the answer that the CSSA specified as right?

Originally posted by Huy
1. This scale/mass question
2. Solarcells and intensity/emf vs threshold frequency (but the answer is intensity/emf because it refers to Einstein's postulate about photons and EM waves being quantised, but both are 'correct', however increasing intensity increases the emf produced is 'more correct' as it was relating to Einstein)

I didnt know there was something wrong with 2? Hope i get marks for it

 

[wogboy]

Do you mean the scale read 40 Kg while you measured your mass here on EARTH, or 40 Kg measured on the moon? Because if that scale was calibrated for EARTH measurements, and on the MOON it said that you were 40 Kg, you must be pretty big fatty (apologies to those who have a mass of 240 Kg ).

 

[underthesun]

Originally posted by wogboy
Do you mean the scale read 40 Kg while you measured your mass here on EARTH, or 40 Kg measured on the moon? Because if that scale was calibrated for EARTH measurements, and on the MOON it said that you were 40 Kg, you must be pretty big fatty (apologies to those who have a mass of 240 Kg ).

In 10 years time, this question will appear on CSSA physics:

With common sense, anybody over 100 kg is considered overweight, and hence should go to Jenny Craig, where in 10 weeks 10 kilos would be shed using Jenny Craig's lite plan.

Kevin travelled to the moon using qantas spacelines and arrived at the Moon Disney Wonderland. He measured himself using a sanyo extra accurate scale designed for earth. It displayed a reading of 30kg.

It is known that the gravity on the moon's surface is 6 times less than the gravity on earth's surface.

Which one of the following is true?

(a) Kevin should go to jenny craig, and he will be considered "normal" in 80 weeks.

(b) Kevin should go to jenny craig, and he will be considered normal in 40 weeks.

(c) Kevin should not go to jenny craig, because no information is known from the Sanyo scale.

(d) As Jenny Craig now offers Weight Gain plan for underweight people, Kevin should register to increase his weight.

 

[jims]

it was on the moon
i feel sorry for that astronaut who weighed 180kg. nasa is really lowering their standards.

cssa specified (b) 50kg as the right answer

and he doesnt mean question 2, that was question 12

 

[@nimal]

Mass stays the same on any surface,
w = m * g
remember, that is one of the core facts you learn

 

[Rahul]

Mass does not change
Earth=> mass=50kg
Mars=> mass=50kg

BUT, gravitational acceleration is different on each planet, g = Gm/(r^2)

But if you are weighed on scales calibrated to a particular planet te scales will read differnetly if you go to a second planet.
eg, Mars=> g_mars=(3.7g)/(9.8g_earth)
Weight of 50 kg on earth scale will read W_mars = mg_mars = 50 x 3.7/9.8 = 18.8kg on mars.

if that doesnt make it clear use this method:

W=mg
on earth, 50 = m x 9.8
on mars, x = m x 3.7

make m the subject in both and equate them. you end up with m = 18.9.

 

[Rahul]

Originally posted by underthesun
Questions
1. You buy a sanyo weight scale, designed for earth.
2. You bring it to moon.
3. The scale reads 40 kg as you stand on it.
Assuming that that the gravity on the moon is 6 times less, what is your mass?
(i'd say 240 kg, but my teacher is saying it remains 40kg)....

w=mg

on moon.... 40 = m x 9.8/6
on earth..... w = m x 9.8

equating both.....240/9.8 = w/9.8

therefore w = 240 kg.

show him this working and ask what is wrong?

Also, tell the teacher to read the question carefully: The scale gave a reading of 50 kg. therefore the weight is 50 kg, not the mass.

the confusing thing is the fact that mass has units, kg. and we use that same unit for weight, practically(not scientifically).

edit: sorry about the double post.

 

[underthesun]

I wholeheartedly agree.

CSSA SUCKS

Originally posted by @nimal
Mass stays the same on any surface,
w = m * g
remember, that is one of the core facts you learn

That thing is the argument my teacher used against me. Plus, he's been saying "he discussed with other teachers from other schools", plus he's taken all the time taken to mark carefully.

obviously make him stupid..

 

[Dangar]

Don't scales on Earth account for gravity? So then to figure out the mass of an object reading 40kg on an earth scale you would have to do F=mg i.e. 40=9.8m
Therefore m=40/9.8
and since the mass remains the same, the mass is around 4

hmmm...ive obviously made some mistake, but where?

 

[underthesun]

the unit for mass is kg, and the unit for weight is Newton.

W = mg, so on earth the weight would be 40 x 9.8 N

but the scale automatically convert the reading to kilograms, by dividing the N value by 9.8

so the reading = W / 9.8 = mg/9.8

Now, on the moon, the g value is 1/6th, so

the reading on the moon should be (9.8 / 6) x m /9.8

= m/6

hence the reading on the moon is 6 times less the actual mass.

 

[dandaman]

mass remains the same wherever you go in the universe.

However weight is a force, measured by Newtons Second Law: F=ma. So to find the weight of this mass, you multiply the 40kg by what ever acceleration due to gravity is relevant (ie Earth would be 9.8m.s-2.

Mass = 40kg
Weight = 392 N