Elevator Problem (HW Check)

  • Thread starter Masrat_A
  • Start date
  • #1
Masrat_A

Homework Statement


A 100kg man stands on a scale in an elevator moving downward. If the elevator decelerates at ##2 m/s^2##, determine the scale reading (in kg).

Homework Equations


##N = -WT = -Mg##

The Attempt at a Solution


##-WT = -100(g)##
##-WT = -100(-10)##
##-WT = 1000##

##Ma = 100(-2)##
##Ma = -200##

##N = -WT + Ma##
##N = 1000 - 200##
##N = 800##

##kg = N/g##
##kg = 800/10##
##kg = 80##

Could any of us please check if this seems correct? Would there be any other possible ways of achieving the answer?
 

Answers and Replies

  • #2
35,724
12,308
If the elevator is moving downwards and decelerating (getting slower), do you expect the scale reading to increase or decrease?
 
  • #3
Masrat_A
If the elevator is moving downwards and decelerating (getting slower), do you expect the scale reading to increase or decrease?

I would expect the scale reading to decrease.

Would ##N = Mg - Ma## be a better formula to use, therefore?

##Mg = 100(10) = 1000##
##N = 1000 - 200 = 800##
##N/g = 800/10 = 80##
 
  • #4
35,724
12,308
I would expect the scale reading to decrease.
Jump up. When you land back on Earth and slow down from the fall, do you legs have to work harder or less hard?
 
  • #5
Masrat_A
Jump up. When you land back on Earth and slow down from the fall, do you legs have to work harder or less hard?

The legs will have to work harder when we land back on Earth.
 
  • #6
35,724
12,308
Right. Correspondingly, a scale would read more.
 

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