Scale in an elevator physics problem

[conniechiwa]

A 62-kg girl weighs herself by standing on a scale in an elevator. What does the scale read when the elevator is ascending at 11 m/s but its speed is decreasing by 5 m/s in each second?

I'm not really sure where to begin.

 

[learningphysics]

A 62-kg girl weighs herself by standing on a scale in an elevator. What does the scale read when the elevator is ascending at 11 m/s but its speed is decreasing by 5 m/s in each second?

I'm not really sure where to begin.

Hint, you need the force exerted by the girl on the scale... that's the weight the scale reads...

You also know that the force the girl exerts on the scale = the force the scale exerts on the girl.

 

[conniechiwa]

Well I know that normally the scale would read 608.5 N if the elevator was not moving, but I'm not sure what to do here.

 

[asd1249jf]

A 62-kg girl weighs herself by standing on a scale in an elevator. What does the scale read when the elevator is ascending at 11 m/s but its speed is decreasing by 5 m/s in each second?

I'm not really sure where to begin.

First, find what the deceleration of the elevator is.

 

[learningphysics]

Well I know that normally the scale would read 608.5 N if the elevator was not moving, but I'm not sure what to do here.

draw the freebody diagram of the girl... what are the forces acting on the girl... you know that \Sigma\vec{F} = ma. follow l46kok's suggestion and find the acceleration of the girl.

 

[conniechiwa]

Would the deceleration be -3.45 m/s squared?

 

[learningphysics]

Would the deceleration be -3.45 m/s squared?

No, the deceleration is the same given in the question...

 

[conniechiwa]

only the velocity is given?

 

[learningphysics]

only the velocity is given?

They give 5m/s per second... so the acceleration is -5m/s^2

 

[BigBadBart]

iidesjo!

okay,

Fg=m*g (Fg is gravitational force)
Girl weighs (m) 62 [kg].
Gravitational constant (g) is 9.81 [m/s^2]
Fg= 62*9.81= 608.22 [N]
that is the static value.

With F=m*a you can calculate the difference in force compared to static (v=c)
a= -5 [m/s^2]
F= 62*-5= -310 [N]

so the scale will indicate 608.22-310= 298.22 [N]
to calculate back to mass divide through the graviotational constant.
298.22/9.81= 30.4 [Kg]
you're welcome!
:D