I thoguht i could just use F=ma but I\'m not sure why I\'m not getting the corre

Question

I thoguht i could just use F=ma but I'm not sure why I'm not getting the correct answers. Please explain the equaion/method used with the process

11. a) A 70-kg woman stands on a bathroom scale in an elevator that is accelerating downward. The scale reads 500 N. What is the magnitude of the elevator's acceleration?

A) 1.58 m/s2

B) 2.12 m/s2

C) 2.66 m/s2

D) 3.08 m/s2

E) None of these

b) A 20.0-kg is dropped from an air-balloon. At a particular instant, its acceleration is measured to be 7.0 m/s2. Determine the force of air resistance on the package at that moment.

A) 28 N

B) 56 N

C) 140 N

D) 196 N

E) None of these

Explanation / Answer

here

F = m * a

500 = 70 * a

a = 7.14 m/s^2

the acceleration of elevator is = 9.8 - 7.14 = 2.66 m/s^2

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