A student\'s backpack, full of textbooks, is hung from a spring scale attached t

Question

A student's backpack, full of textbooks, is hung from a spring scale attached to the ceiling of an elevator. When the elevator is accelerating downward at 3.5 m/s2, the scale reads 48 N. (a) What is the mass of the backpack (in kg)? 7.62 (b) What does the scale read (in N) if the elevator moves upward while slowing down at a rate 3.5 m/s2? (c) What does the scale read (in N) if the elevator moves upward at constant velocity? If the elevator had no brakes and the cable supporting it were to break loose so that the elevator could fall freely, what would the spring scale read (in N)? (d)

Explanation / Answer

b) 48 Newton

As it is slowing down in upward direction so it is deaccelerating in upwad direction

For downward acceleratino:

m(g-a) =48, m(6.3)=48,m=48/6.3=7.62 kg

C) 74.68 Newton

for constant velocity it will show actual weight =mg

=9.8*7.62=74.68 N

D) 0 Newtom

In case of free fall it will show no weight as both will accelerate will same acceleration g

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