Force Question: student mass in elevator accelerating & coming to a stop

[kgarcia654]

Homework Statement

A student of mass 52 kg stands on a bathroom scale in an elevator that is accelerating at 0.60 m/s². The elevator is descending and coming to a stop at a floor. What does the scale read? (Start by deciding what direction the acceleration is.)

Homework Equations

f=ma

The Attempt at a Solution

31?

 

[Chi Meson]

No.

First of all, what unit goes with 31? Regardless of your own bathroom scale, pretend you are using one that measures in Newtons (SI unit of force).

How much is the weight going to be normally?

Think about being in an elevator, going down, and the elevator is coming to a stop. As it is stopping, briefly, do you feel slightly heavier or slightly lighter?

 

[ogb p]

I would first clarify that the question is asking for the reading on the bathroom scale, which is measuring the normal force exerted by the student on the scale. The acceleration in this scenario is downwards, as the elevator is descending. Using the equation f=ma, we can calculate the normal force by multiplying the mass (52 kg) by the acceleration (-0.60 m/s²). This gives us a normal force of -31.2 N, which means the scale would read 31.2 N. However, since the scale is typically calibrated in units of weight (N or kg), we would need to convert the normal force to weight by dividing by the acceleration due to gravity (9.8 m/s²). This gives us a scale reading of -3.18 kg, which would be rounded to -3.2 kg. Therefore, the scale would read -3.2 kg, indicating that the student's weight has decreased due to the downward acceleration of the elevator. Once the elevator comes to a stop, the scale reading would return to the student's actual weight of 52 kg.