Physics Help Forum AP Physics Elevator Problem

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Dec 12th 2010, 02:38 PM #1 Junior Member   Join Date: Dec 2010 Posts: 1 AP Physics Elevator Problem I'm really not sure if I'm doing this problem even remotely correct... The Problem: An elevator starts from rest and after 3 seconds of constant acceleration reaches a velocity of 5 m/s going up. What is the normal force of the floor on a 110 kg person standing in the elevator. My attempt: (I've bolded forces, subscripts lowercased) v=u+at 5m/s=a(3s) 1.667 m/s^2 = a Nep=Ffp-Fep =ma+mg =m(a+g) =110kg(1.667-9.8) =894.63N
 Dec 13th 2010, 01:16 AM #2 Physics Team     Join Date: Jun 2010 Location: Mauritius Posts: 609 One question for you, do you feel heavier when going up an elevator or lighter? Because in the solution you got, you mean to say that you feel lighter Let's verify the forces on the person. Normal Force - Weight = Net force Where the normal force is upwards, the weight downwards and the net force upwards. g and a already have their correct signs. F - mg = ma F = m(g + a) As the magnitude of acceleration is larger and you feel heavier when going up! __________________ Jerry (Got my results!) It is easier to protect your feet with slippers than to cover the earth with carpet. No one can go back and change a bad beginning; but anyone can start now and create a successful ending. If a problem can be solved, no need to worry about it. If it cannot be solved what is the use of worrying?

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