Answer:
a) a = 4 ft / s²
, b) a = -6 ft / s²
Explanation:
The balance is subjected to two forces: the weight of the person directed downward and the spring reaction directed upward.
When the person rides the elevator, the acceleration is zero
F - W = 0
F = W
F = 160 lb
let's find the mass of the body
W = mg
m = W / g
m = 160/32
m = 5 slug
A) when the elevator is moving up
F - W = m a
F = W + m a
F - W / m = m a
F = m (g + a)
therefore the scale reading (F) must be higher, in this case F = 180 lb
a = F / m - g
a = 180 - 160)/5
a = 4 ft / s²
b) when the elevator is stopping
in this case the direction is opposite to the speed, that is to say downwards
F- W = m (-a)
a = W - F / m
a = 130 -160 /5
a = -6 ft / s²
