Acceleration of an elevator with different readings on the weighing scale (7068)

, por F_y_Q

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A person with a mass of 70 kg stands on a weighing scale in a moving elevator and observes different readings. Determine the acceleration of the elevator and wether it is moving up, down, accelereting, decelerating or stationary if the scale readings are: a) 66 kg, b) 74 kg and c) 70 kg.

P.-S.

Weight and normal force have opposite sense and the following equation is used:

p - N = m\cdot a\ \to\ \color[RGB]{2,112,20}{\bm{a= \frac{(m - m^{\prime})\cdot g}{m}}}

Just substitute the values and calculate the acceleration in each case:

a)

a = \frac{(70 - 66)\ \cancel{kg}\cdot 9.8\ \frac{m}{s^2}}{70\ \cancel{kg}}= \fbox{\color[RGB]{192,0,0}{\bm{0.56\ \frac{m}{s^2}}}}


The elevator is moving down.

b)

a = \frac{(70 - 74)\ \cancel{kg}\cdot 9.8\ \frac{m}{s^2}}{70\ \cancel{kg}}= \fbox{\color[RGB]{192,0,0}{\bm{- 0.56\ \frac{m}{s^2}}}}


The elevator is moving up.

c)

a = \frac{(70 - 70)\ \cancel{kg}\cdot 9.8\ \frac{m}{s^2}}{70\ \cancel{kg}}= \fbox{\color[RGB]{192,0,0}{\bm{0\ \frac{m}{s^2}}}}


The elevator is not moving.