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Forces : Man in a lift on a scaler 
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#1
Nov909, 10:42 AM

P: 15

1. The problem statement, all variables and given/known data
A man of mass 70 kg stands in a lift on a set of weighing scales. The scales are calibrated in newtons. Assuming that g=10N kg 1 What weight will the scales register when the : a) lift is static b)lift accelerates down at 10 ms2 c)lift accelerates up at 10 ms2 2. Relevant equations F=ma 3. The attempt at a solution a) F=ma F= 70 x 0 F=70 b) accelerates down at 10ms 2 F=ma F=70 /10 F=7 707=63 c) accelerates up at 10 ms 2 70 + 7 = 77 Is this correct ? Thanks, dave 


#2
Nov909, 01:42 PM

P: 15

Can someone please help me ?



#3
Nov909, 01:46 PM

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P: 41,436

Don't forget to give your answers in Newtons, not kg. 


#4
Nov909, 01:53 PM

P: 15

Forces : Man in a lift on a scaler
I don't understand you, sorry. Can you explain again please ?
Is F=ma all I need here ? I am not sure, however I really want to solve it :) 


#5
Nov909, 01:56 PM

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#6
Nov909, 02:02 PM

P: 15

So I think it would be gravity acting down and also the normal force pushing him up, correct ?
Knowing that in the first case I subtract and in the second case I add the forces right ? However I still do not get the connecting between 'g' and the question. :( 


#7
Nov909, 02:12 PM

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#8
Nov909, 02:26 PM

P: 15

Ill try do a then :
if the GF is pushing him down and NF is pushing him up then his weight is 70N cause the gravity force is greater by 70 N Second one: If the lift is going down then the gravity force must he smaller by 10 : 7010 = 60 N Third one : vice versa 70+10=80 N Am I thinking correct at this time ? By the way I really appreciate your help and patience here. 


#9
Nov909, 02:29 PM

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#10
Nov909, 02:31 PM

P: 15

it must be zero cause hes not going up, right ?



#11
Nov909, 02:36 PM

P: 29

The man is 70 kg, and there's a gravitational force acting down on him, with this in mind F=m(man)*a(???) even though the elevator isn't accelerating what other acceleration is there?
Keep in mind gravity is in m/s^2. 


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