Find the acceleration of the elevator.

[badboyben03]

how can i find the answer w/o knowing the mass?

A student stands on a bathroom scale in an elevator at rest on the 64th floor of a building. The scale reads 818 N. As the elevator moves up, the scale reading increases to 950 N, then decreases back to 818 N. Find the acceleration of the elevator.

 

[redrogue]

Actually you can solve for the mass of the person when he is at rest. At rest, acceleration is due to gravity so:

$$F_{1}=mg$$
and
$$m=\frac{F_{1}}{g}$$

where $$g=9.81\frac{m}{s^2}$$ and $$F_{1}=818N$$.

 

[badboyben03]

after i find the mass of the person? wut do i have to do?

 

[redrogue]

950N is the normal force the person experiences.

The person's weight must be subtracted out to get the net force which is 950N-818N=132N.

Using Newton's 2nd Law, we can can find the acceleration.

$$F=ma$$

implies

$$a=\frac{F}{m}$$

where F =132N and m is the mass of the person found.