Physics

posted by .

When I asked my teacher for help he told me this

This is a logical puzzle. Having 75% of the typical weight means experiencing 75% of the typical gravity. The floor must be falling away with an acceleration of 25% of typical gravity.

Here's the question I asked that's from my textbook

A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only .75 of the person''s regular weight. Calculate the acceleration of the elevator, and find the direction of acceleration.

ok isn't weight by defintion the force of gravity which is equal to mass time gravity how could this every change? I understand that in this situation the net force change but no the actual weight so I'm lost... I'm know the normal force exerted by the scale onto the person would change becasue the acceleration changes and for a brief moment weighs less than she would without going in the elevator...

so I'm the normal force exerted by the scale onto the person would obviously change but how would her weight change?

Can you explain to me how to do this problem or as to why I can do this problem this way because I do not understand it. Thanks

  • Physics -

    Her weight doesn't change, but her so-called "apparent weight" does change:

    http://en.wikipedia.org/wiki/Apparent_weight

  • Physics -

    "how would her weight change?"
    The force of weight we sense is actually the normal force, or the force pushing us up. If the elevator accelerates downward, that force is reduced, as is our perception of our weight.

    By Newton's 3rd law, the sum of the forces acting on the person equals the mass times acceleration.

    sum(F) = ma.
    the sum of forces also equals the normal force + the force of weight.

    sum(F) = Fn - Fw

    When the person is at rest, the sum of the forces = 0.

    0 = Fn - Fw

    However, when the elevator accelerates downwards, the Fn is only .75 of what it was.

    sum(F) = .75Fn + FW

    ma = .75mg - mg

    a = .75g - g
    a = -.25g

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Physics

    A typical brick has dimensions of 20.0 cm by 10.0 cm by 5.0 cm and weighs 20.0 N. How does the pressure exerted by a typical brick when it is resting on its smallest side compare to the pressure exerted when it is resting on its largest …
  2. english

    what means typical and typical person? http://www.onelook.com/?
  3. physics

    Hi i'm doing that lab were you attach a weight to a tape which is also through a timer that puts marks on the tape at a given time interval ok I'm asked why is gravity different than on Earth?
  4. physics

    Calculate the acceleration due to gravity on the moon. The moon\'s radius is about 1.74 E 6 m and its mass is 7.35 E 22 kg ok aparently there\'s an easier way to do this I applied Newtons second law in the radial direction net force …
  5. Physics

    A 75 g autographed baseball slides off of a 1.3 m high table and strikes the floor a hori- zontal distance of 0.65 m away from the table. The acceleration of gravity is 9.81 m/s2 . What was the direction of the ball’s velocity just …
  6. physics

    1. What is a typical drift speed of electrons that make up a current in a typical DC circuit?
  7. Physics

    A) Gravity pulls an area of wet soil and rock downward in a landslide B) An ... Many people know that the weight of an object varies on different planets, but did ... If the Earth's gravitational force causes a falling 74 kg student …
  8. Curriculum Development

    Alex was working on a Blues Clue puzzle.This was the favorite puzzle of all of the children in the room.After observing him for a while, his teacher, Mrs.Obrecht, believed that Alex might be experiencing an eye-hand coordination problem.She …
  9. physics

    A light–rail commuter train draws 645 A of 590–V DC electricity when accelerating. What is its power consumption rate in kilowatts?
  10. physics

    a typical person can tolerate an acceleration of about -49m/s2 (forward). If you are travelling at 110km/h and have a collison with a solid immovable object, over what minium distance must you stop so as to not exceed this acceleration

More Similar Questions