WPM Physics

[Mavs88]

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1. A man (mass 150 kg) is standing on a scale in an elevator which is dropping free fall. According to the scale, how much does he weigh? g = 10 m/s2
   
   1. 150 N
      
      
   2. 1500 N
      
      
   3. 15 N
      
      
   4. 0 N
      
      -The answer is 0 N...not sure how.
      
      
      

 

[NicMouse64]

1. A man (mass 150 kg) is standing on a scale in an elevator which is dropping free fall. According to the scale, how much does he weigh? g = 10 m/s2
   1. 150 N
      
      
   2. 1500 N
      
      
   3. 15 N
      
      
   4. 0 N
      
      -The answer is 0 N...not sure how.
      
      

Draw an FBD, think about the forces. The normal force will be negligent and therefore will not have a reading. HOWEVER, if the elevator were going up the weight would be MA(150*10=1500). Think about a roller coaster, when you get to the bottom of a drop you feel weightless right? This is the same concept.

 

[Quinoline]

Draw an FBD, think about the forces. The normal force will be negligent and therefore will not have a reading. HOWEVER, if the elevator were going up the weight would be MA(150*10=1500). Think about a roller coaster, when you get to the bottom of a drop you feel weightless right? This is the same concept.

If the elevator were going up at a constant velocity the scale would read 1500 N.
If the elevator were accelerating up, the scale would read 1500+150*a N

The scale reading is Fn and Fn=mg+ma. In the case of free fall, a=-g so Fn=0

 

[Mavs88]

Thank you!