Calculate the acceleration of the elevator

AI Thread Summary
To calculate the acceleration of the elevator, the equation F_normal - mg = ma is used, where F_normal is the force read by the scale, mg is the person's weight, and a is the acceleration. When the scale reads 0.78 of the person's weight, it indicates that the elevator is accelerating downward. By substituting the values into the equation, the acceleration can be determined. The direction of acceleration is downward, as indicated by the reduced reading on the scale. Understanding the derivation of the equation helps clarify the relationship between forces acting on the person in the elevator.
bpw91284
Messages
67
Reaction score
0

Homework Statement


A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads
only 0.78 of the person’s regular weight.
a. Calculate the acceleration of the elevator.
b. Find the direction of acceleration.

Homework Equations


Sum of forces.

The Attempt at a Solution



I know the equation is F_normal-mg=ma but don't understand how it was derived.
 
Physics news on Phys.org
The normal force points in the y direction and is opposite to the weight of the person (mg). Newtons law says that the sum of all forces = ma. Since the elevator is only moving in y direction, the only component of the net force is the component in the y direction. Put the 2 together and you have F_n -mg = ma

Now that you know this...what are your thoughts on the problem?
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Calculating Elevator Acceleration: Solve for F=ma
Replies
3
Views
2K
Pushing a block against the wall of an elevator that is accelerating
Replies
42
Views
2K
Calculate elevator acceleration using mass
Replies
9
Views
4K
Elevator Motion and Bathroom Scale Readings
Replies
2
Views
2K
Find the power needed to accelerate this elevator downward
Replies
4
Views
1K
Mechanics: Elevator Accelerating Downward
Replies
10
Views
4K
Acceleration of Body in Elevator & Earth with 0.5g Rise
Replies
12
Views
2K
Understanding Sign Conventions in Elevator Tension Problems
Replies
6
Views
3K
Calculate Elevator Accel. - FN=mg+ma
Replies
1
Views
2K
Forces, elevator, acceleration -- I have the answer, just explain it....
Replies
2
Views
12K

Hot Threads

Recent Insights

Back
Top