# physics 12 - dynamics

Hi, I'm just confused as to what steps to take in order to solve these problems.
If you could please show your steps and method on how to approach these questions to get the answer that would be great. I have the answers to these too, if needed. I want to know how to solve them though.

1) An elevator (mass 4850kg) is to be designed so that the maximum acceleration is 0.0680g. What are the maximum and minimum forces the motor should exert on the supporting cable?

2) A person stands on a bathroom scale in a still (motionless) elevator. When the elevator begins to move, the scale briefly reads only 0.75 of the person's regular weight. Calculate the acceleration of the elevator and find the direction of acceleration.

3) a)What is the acceleration of two falling sky divers (mass 132kg) when the upward force of air resistance is equal to one-fourth of their weight?
b) After popping open the parachute, the divers descend leisurely to the ground at constant speed. What now is the force of air resistance on the sky divers and their parachute?

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1. Net force on mass = mass * acceleration

1)
accelerating up
T - 4850*9.8 = 4850 *.068
accelerating down
T - 4850*9.8 = -4850*.068

2) define up as +
- m g + .75 m g = m a
so
a = -.25 g
accelerating down

3)a) 132 *9.8 - .25*132*9.8 = 132 a

b) 132*9.8 -air resistance = 132*0

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