Homework Help: physics

Posted by Sasha on Monday, October 26, 2009 at 9:27pm.

When will your apparent weight be greatest, as measured by a a scale in a moving elevator; when the elevators: (a) accel. downward (b) accel. upward (c) is in free fall (d) moves upward at a constant speed? In what case would you weight be the least? When would it be the same as when you are on the ground?

physics - bobpursley, Monday, October 26, 2009 at 9:42pm
Think about it.

weightapparent=mg+ma where a is up. What if a is down? What if a=-g?
physics - MathMate, Monday, October 26, 2009 at 9:44pm
Apparent weight
= m(g+a)
where g=9.8 m/s²
a=acceleration, positive upwards.
(a) W=m(g-|a|)
(b) W=m(g+|a|)
(c) W=m(g-|g|) = 0
(d) W=m(g+|0|) = mg
physics - Sasha, Monday, October 26, 2009 at 9:47pm
so the it would be the least on the way down, b/c your force, pushing on the scale is less. And it is greatest on the way up, since your force of push is stronger. And I would say in free fall it is the same as ground state?
physics - MathMate, Monday, October 26, 2009 at 9:48pm
Rethink free-fall.
physics - Sasha, Monday, October 26, 2009 at 9:55pm
ohh okay so the weight would be the same on the ground if its moving up at a constant speed?
physics - MathMate, Monday, October 26, 2009 at 9:58pm
Exactly. When it moves upwards (or downwards) at a uniform velocity, the reaction on the floor is the same as the weight. You have probably experienced this when you ride on an elevator.
physics - Sasha, Monday, October 26, 2009 at 10:04pm
sweet!! thank you =)
physics - MathMate, Monday, October 26, 2009 at 10:07pm
You're welcome!

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