Forces Problem in an elevator

  • #1

Homework Statement



You are standing on a spring balance in an elevator. Draw a graph of scale balance reading VS time. At T0 you are at rest, accelerate upwards until T1 (where you reach constant speed) then decelerate from time T2 to T3.

Homework Equations



N/A

The Attempt at a Solution



So I know that the scale reading will go up when accelerating upwards because the net force must be upward, so the normal force is greater than mg. But, once it goes at a constant speed (T1) will the reading go back to original mg, or will it remain at the higher reading until it begins to decelerate again?

Thanks.
 

Answers and Replies

  • #2
gneill
Mentor
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2,866

Homework Statement



You are standing on a spring balance in an elevator. Draw a graph of scale balance reading VS time. At T0 you are at rest, accelerate upwards until T1 (where you reach constant speed) then decelerate from time T2 to T3.

Homework Equations



N/A

The Attempt at a Solution



So I know that the scale reading will go up when accelerating upwards because the net force must be upward, so the normal force is greater than mg. But, once it goes at a constant speed (T1) will the reading go back to original mg, or will it remain at the higher reading until it begins to decelerate again?

Thanks.
Draw the free body diagram for the "coasting" (constant speed) case. What's the net force on you?

Hint: Suppose the elevator has a particularly smooth and noiseless mechanism, and the floor counter and button lights were masked from you. Would you be able to distinguish between coasting at some constant speed and being at rest?
 
  • #3
PhanthomJay
Science Advisor
Homework Helper
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If the scale reading remained at the higher reading between T1 and T2, the normal force would be greater than mg. What can you conclude from that?
 
  • #4
ohhh so since constant velocity, the net force is zero, so they must balance out again right?
 
  • #5
PhanthomJay
Science Advisor
Homework Helper
Gold Member
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507
ohhh so since constant velocity, the net force is zero, so they must balance out again right?
Right.
 

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