Question

Determine the magnitude of the apparent weight of a 56 kg student standing in an elevator when the elevator is experiencing an acceleration of (a) 3.2 m/s^2 downward and (b) 3.2 m/s^2 upward.

Answer 1

W = m*a
When it's going up, acceleration is: g+a, when it's going down acceleration is g-a

Answer 2

a) total a = -9.8-3.2 = -13
W = 56*(-13)N

Answer 3

You see, here's what I did for a and b.

Answer 4

b) total a = -9.8 + 3.2 = -6.6
W = 56*(-6.6)N

Answer 5

a) f=ma
=(56)(3.2+9.81)
=728.56N

Answer 6

Why is the force negative in both cases?

Answer 7

because weight is pushing down.

Answer 8

Ok. Give me a second to redo this...

Answer 9

same thing, just change the signs

Answer 10

you found the normal force, which has the same magnitude, but opposite direction

Answer 11

And its alright if my signs are negative? Because the answers are A) 3.7*10^2N and b) 7.3*10^2N

Answer 12

ohh yea they asked for magnitude. If they just asked for weight, ur answers wld be negative

Answer 13

since weight has magnitude and direction. In this case it's going down, hence the negative.

Answer 14

k. ill work with this. if i need help, ill call out

Answer 15

Hey @bahrom7893 ?

Answer 16

hey

Answer 17

the answer for A) was wrong. you probably explained this, but i forgot

Answer 18

We got -728.56N. The book says 3.7*10^2N

Answer 19

Wait in the answer, is the answer for a greater than the answer for b?

Answer 20

No.

Answer 21

A) 3.7*10^2N and b) 7.3*10^2N
Aren't those the answers?

Answer 22

yup

Answer 23

oh yea.. obv. Hang on I know what we did wrong

Answer 24

for A), i did this: "56)(-3.2-9.81)

Answer 25

well it makes sense.. i just always confuse the signs of g. g has to be positive in this case.

Answer 26

would that make my value of 3.2N positive too?

Answer 27

http://www.intuitor.com/student/elevatorrProblem.php

Answer 28

it's the sign of g, i always get confused with it..

Answer 29

am I to consider 3.2N a positive or negative force?

Answer 30

well is it pushing down or up?

Answer 31

It's pushing down

Answer 32

If it was -ve, it would make sense mathematically, but not in terms of real world physics(for me)

Answer 33

then it's negative, but they're just asking for magnitude, or abs value of that force.

Answer 34

https://docs.google.com/viewer?a=v&q=cache:xp0UsLqIQAEJ:pleasanton.k12.ca.us/avhsweb/barnettdreyfuss/Physics/Documents/ElevatorHelp.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEESgOMe38l7ow_fcC2jk4lULurodnv-4-vaORTq16eM87K7SLxLuGYv2O-HfEbFZyYeZwSx-qhMcpD5rNKvzT9Mr5TpwR1yAX_zgPO91ur3XVwrnSJ547HJqi-Z4aRe3xpDrjv1vn&sig=AHIEtbQpU7-PDOl_gkxu6JaT3QyU2AZ31w

Answer 35

ok. give me a moment to readi guess