Q. A $60\ kg$ man stands on a spring scale in the lift. At some instant he finds, scale reading has changed from $60\ kg$ to $50\ kg$ for a while and then comes back to the original mark. What should we conclude
A) The lift was in constant motion upwards
B) The lift was in constant motion downwards
C) The lift while in constant motion upwards, is stopped suddenly
D) The lift while in constant motion downwards, is suddenly stopped
Explanation
(c) For upward acceleration apparent weight $= m(g + a)$
If lift suddenly stops during upward motion then apparent weight $= m(g - a)$ because instead of acceleration, we will consider retardation
In the problem it is given that scale reading initially was $60\ kg$ and due to sudden jerk reading decreasing and finally comes back to the original mark $i.e.$ , $60\ kg$
So, we can conclude that lift was moving upward with constant speed and suddenly stops
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.