Elevator Cable and Tension?

Question

An elevator with a weight of 27.9 kN is given an upward acceleration of 1.68 m/s2 by a cable.

(a) Calculate the tension in the cable.
_________ N
(b) What is the tension when the elevator is decelerating at the rate of 1.68 m/s2 but is still moving upward?
____________N

Can anyone help me start and help me work through this? I am just having trouble with it in general.

Answer 1

Recall Newton's three Laws. you really need to understand them, get familiar with them, and frequently use them.

elevator with a weight of 27.9 kN. Weight is a force due to gravitational accelaration: W = m*g, with g = 9.81m/s^2. Given W, you can easily find m.
(a) F = ma. Given a and knew m, you can figure out F. Note: cable tension is F + W, since with tension W in the cable the elevator would not move up or down.

(b) decelerating is accelaration downward. Again take "a" positive we have:
f = m(-|a|) and f + W is the tension.

You can put in all numericals.

Answer 2

m = F/a = 200E5 / 9.eighty one = 20.4E5 kg (3 sig figs) T = 200E5 + 20.4E5 * 3.00 = 261E5 N Conversely...you are able to upload the acceleration of the elevator and the gravity. Atot = 9.eighty one + 3.00 = 12.8 T = 20.4 * 12.8 = 261E5 N Hehe...acceptable Trevor...this is one hefty elevator!