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Elevator and mass of a student help

  1. Jul 26, 2009 #1
    1)A student weighing 735 N steps into an elevator and pushes the button to go up. If the elevator accelerates at 3.5 m/s2 for 3.0 s, what is the mass of the student during this time?

    2)f=ma, v=d/t

    3)i dont quite understand how the student can weigh 735 N and consequently I'm completely lost on this question.
  2. jcsd
  3. Jul 26, 2009 #2


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    Homework Helper

    Re: Mass

    Well, do you know what a Newton is? It's a unit of force, like a pound. Saying that a student weighs 735 N is the same as saying that the student weighs 165 pounds. (One pound is equal to about 4.45 Newtons; this is a value you can look up.)

    If it helps you solve this problem, use the weight of 165 pounds to figure out the student's mass. But if you do, you should probably go back and do it again without converting the student's weight into pounds. Get used to Newtons, because as long as you're doing physics, you're going to see them a lot.
  4. Jul 26, 2009 #3


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    Science Advisor

    Re: Mass

    Was that really the question? If the student weighs 735 N, then use F= mg so m= F/g= 735/9.81 to find the mass. Mass doesn't change if you are on an elevator.

    IF the problem said that his weight on the elevator was 735 N, then you could use 735= m(9.81+ 3.5) to find his mass.
  5. Jul 26, 2009 #4
    Re: Mass

    thank you both of you! :D
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